In order to be elevate a basic user to Power User you must first be logged in as the administrator.

This can be confirmed by the Configuration  menu in the upper right.

A Power User is a basic user with the Skill of Steward.
Before a Steward cna be elevated to Power User the skill of Steward must be punched down via the SKILL section or by editing the skills of the User Profile.

Skills Section

Edit User Profile

Click on Configuration in the upper right
Click on Manage Powerusers  on the left

Search for the Available Steward for the Add New Powerusr form

Click outside the results box and the click Promote

Delete A Power User
Select the Poweruser from the list of Active users and hit Delete.

This does not delete the employee, just removes the access rights.