uninstall 3rd party antivirus

Dear Team,

We are moving from Sophos 10.3 to Symantec. We have setup the Symantec Endpoint Managment server 12.1.6. We want to automatically uninstall the Sophos 10.3 antivirus and install Symantec antivirus. How can we do it in SEPM.
and also few clients have Avast premier i tried with sepprep tool but unable to understand if any one can help it will be a great help for me