The user who should become the account owner should already have an active user profile on the account. Then the current account owner can follow these steps to change things over --
Go to Account Settings > Subscription > Plans and Billing.
Scroll under the plan options and you will see the block for Ownership.
In the dropdown, select the user who should be the new owner.
Select the Update button to complete the change.
** Users will need to sign out and back in to see the changes reflected.