If you purchased on Google Play Store:
Google doesn't currently provide a way to transfer paid apps from one account to the another.
Still, you can add your "old" account to Android Settings => Accounts on your device and select this account in Play store app (side menu => right top arrow next to Google account), then restart Poweramp.
If you purchased on Poweramp website:
It's not required to change anything - please just use your old email + PayPro Order ID to activate the Full Version.
Google doesn't currently provide a way to transfer paid apps from one account to the another.
Still, you can add your "old" account to Android Settings => Accounts on your device and select this account in Play store app (side menu => right top arrow next to Google account), then restart Poweramp.
If you purchased on Poweramp website:
It's not required to change anything - please just use your old email + PayPro Order ID to activate the Full Version.