As long as the level is not activated, it won't be an option. To manually set a user to it, edit their account and select the new level from the membership level options on the right of the profile edit page. Make sure to set the duration for the level to unlimited.
To set a user as admin (full admin panel access), there's no way to do this right now from the interface. It should be in the next feature release. You'll need to edit their profile from the database, and change their Role number to 3.
These market extensions can also allow you to set users as admins:
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