To change Admins on your Enterprise Account, you will need to transfer the current email address on the account to your new admin's email address.
To do this, login to your Admin Account and click My Account:
After clicking My Account, scroll down to the bottom of the page and click Transfer Admin Account.
On this page, Fill out the details of the person you would like to transfer admin access to including their name and email address and click Transfer Account.
Once you click Transfer Account, an email will be sent to confirm your new admin's email address. This email will also prompt them to change the password for the admin account.
Once the email address is confirmed and the password is changed, your Enterprise Account transfer will be complete!