The easiest way is to register your email address with your PVZ2 account. This is done by clicking the cloud button on the main menu.
Since the recent update seems buggy, I would recommend taking a note of your player ID BEFORE you do anything to your account just incase.
Below is what I did when I changed my phone.
Register my email with EA on the currently (old) device if not yet done so. There is also an incentive of 100 free gems.
Once this is done, my PVZ2 account is tied to my email.
When i installed the game on my new phone, I registered again with the same email address, I received a code to confirm I am the account holder, after this, I was given a choice to load my old account (with all the game saved progress) over to the new phone.
Important note: When given a choice after identity conflict, please do make sure to select the account with the same player ID as your old phone and NOT to start a new one as if you are knowing starting a new one, this would replace your original account and you will have to start all over from the beginning as a new player.
Hope this helps
