how to modify my build.xml file and package.xml file as required to deplo only changes.

 package.xml file
 ------------------

 <?xml version="1.0" encoding="UTF-8"?>
<Package xmlns="http://soap.sforce.com/2006/04/metadata">
<types>
    <members>*</members>
    <name>ApexClass</name>
</types>

<types>
    <members>*</members>
    <name>ApexPage</name>
</types>
<types>
    <members>*</members>
    <name>ApexTrigger</name>
</types>
<types>
    <members>*</members>
    <name>StaticResources</name>
</types>
<version>41.0</version>

<property file="build.properties"/>
<property environment="env"/>

<target name="deploy">

    <sf:deploy username="${sf.username}"
                 password="${sf.password}"
                 serverurl="${sf.serverurl}"
                 runAllTests="true"
                 logType="Detail"
                 deployRoot="src"/>

</target>