How to add an extra Device Admin on Nexus 7

[lockey813]

I have a Nexus 7 and 2 accounts installed (only 1 is admin access = owner account). I have noticed the need to grant admin access to both accounts, but I have no idea on how to do that. If I go to settings/security/Device Administrators it says "No available device administrators", there is no option here to add. Please help. Thank you

If I can only have 1 device admin, then how can I change it to the other account (without having the delete/wipe my data)