The owner of an employer is the only user that can remove other users and manage billing.
If you are the owner of an employer then you can transfer ownership to another user.
First ensure that you've invited the new owner and given them the Admin role.
Once they have accepted your invite they'll be listed on the Users page.
At the bottom of the Users page is a "Change Ownership" button.
Click it and choose the new owner. Click the button to confirm.
The selected user will now be the owner of the account.