It's easy to edit an Admin user's contact information. Follow these steps:
Head over to the Users page > Admins
Click on the pencil icon beside the user to edit
Here you can edit the following information:
Name
Title
Email address
Cell phone number
Role/Permissions
Locations
Email notifications
You can also reset the authentication by clicking on "Authentication" in the bottom-right corner.
NOTE: Be careful when editing an Admin user's role. If you change a main Admin role, that role will be changed for EVERYONE who has the role, not just for the person you are editing! If an Admin user needs different permissions, create a new role for that person.