You can remove the mail shield for each client in the group by going to the console. Remember all policy changes or edits must be done through the console or they will be undone if applied directly on the client. Once in the console, right click on the computer group and go to PROPERTIES, from their you can change the installation package of the group then run an update to update the clients with the new policy change.
If you still have some questions about this please refer to your user manual which can be found in the AEA Installation Guide in the forum or contact edu@avast.com for additional help.
Kind Regards