Tested with Android 5.1 firmware 1.2.9.0
If you need to delete Google account / change Google password, or just reset Play Store for any reason here is how:
1. Delete any existing Google account: Settings - General - More settings - Accounts - Google - YOUR ACCOUNT NAME - top right menu: Remove account (you need a pointing device for this).
2. Settings - General - More settings - Apps - Google Play services - UNINSTALL UPDATES.
3. Settings - General - More settings - Apps - Google Play - UNINSTALL UPDATES.
4. Reboot A5. After reboot leave it for 5 minutes. Android will be reconfiguring itself in the background.
5. Run Play Store and sign in.