<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0206</schemaVersion>

    <documentType>3/A</documentType>

    <periodOfReport>2021-05-19</periodOfReport>

    <dateOfOriginalSubmission>2014-12-23</dateOfOriginalSubmission>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001505155</issuerCik>
        <issuerName>Upland Software, Inc.</issuerName>
        <issuerTradingSymbol>UPLD</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001477025</rptOwnerCik>
            <rptOwnerName>ESW Capital, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>401 CONGRESS AVE, SUITE 2650</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>AUSTIN</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>78701</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001295389</rptOwnerCik>
            <rptOwnerName>LIEMANDT JOSEPH</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>401 CONGRESS AVE., SUITE 2650</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>AUSTIN</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>78701</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001813186</rptOwnerCik>
            <rptOwnerName>DevFactory FZ-LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>401 CONGRESS AVE., STE 2650</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>AUSTIN</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>78701</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1803574</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">It was recently discovered that the transfer of these shares from DevFactory FZ-LLC (&quot;DevFactory&quot;), a controlled subsidiary of ESW Capital, LLC (&quot;ESW&quot;), to Acorn Performance Group, Inc. (&quot;Acorn&quot;), a subsidiary controlled by ESW, in 2014 was not completed; therefore, the original Form 3, as amended on December 23, 2014, and all subsequent Form 4s up to the date of this filing, identified Acorn as the beneficial owner in error. These shares were held directly by DevFactory. Joseph A. Liemandt is the sole voting member of ESW and may be deemed to have beneficial ownership, for purposes of Section 13(d) of the Securities Exchange Act of 1934, of the shares held by ESW and DevFactory. Mr. Liemandt disclaims Section 16 beneficial ownership of the shares held by DevFactory, except to the extent, if any, of his pecuniary interest therein, and ESW disclaims Section 16 beneficial ownership of the shares held by DevFactory, except to the extent, if any, of its pecuniary interest therein.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Andrew Price, Chief Financial Officer of ESW Capital, LLC</signatureName>
        <signatureDate>2021-05-24</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Andrew Price, Attorney-in-Fact for Mr. Joseph A. Liemandt</signatureName>
        <signatureDate>2021-05-24</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Rahul Subramaniam, Manager of DevFactory FZ-LLC</signatureName>
        <signatureDate>2021-05-24</signatureDate>
    </ownerSignature>
</ownershipDocument>
