Only the current Account owner can transfer the role of Account owner to a different team member. In order to transfer the account ownership, the account owner needs to log in and navigate to “My Team”.
Identify the new Account owner within existing team members or invite a new team member and click the action menu to select “Make Account owner”. A newly invited member must first accept the invitation on their email, before you can transfer the ownership. Once they accept the invite you'll see a status change on your new team member.