This article assumes that you've already added the person to you app. If not, please have a look here first: http://help.timekit.io/introducing-timekit/setting-up-timekit/how-do-i-add-more-usersresources-to-my-account
Navigate to your app settings via the lower left menu.
Search for the name of the person your wish to "upgrade" to become an admin
That's it 💪
The person now has full access to control your app, including updating billing information, changing name and creating new resources.