They are also the owner of the account data so the owner should be the person who is paying for Follow Up Boss and the leads in the system.
Things to be aware of when changing account ownership:
Inbox Lead Processing (pulling in new leads) is only active for the account owner. If you process leads via the current account owner's email, you will need to change those leads to go to the new account owner's email. After you receive leads through the new email, you should check the lead flow screen to confirm that it is set up how you would like.
The new account owner will control the account in terms of billing, cancelling, export permissions, etc.
Changing account ownership:
Send an email to firstname.lastname@example.org from the current account owner requesting the change.