Hello MS,
You can delete the backup using GUI or CLI. This will delete the backups from primary and from secondary, if protected.
If using Snapmirror relationship between primary and secondary, you can even free the backup from primary. the protected backup will get deleted from Secondary when the next transfer occurs.
De-activating protection policy by setting it back to none will remove the datasets created by SMO in protection Manager and eventually clean up the SM/SV relationship of the objects.
Thanks,
Himanshu