You have to be an Administrator to change another user's permission!
Steps:
Navigate to the Manage users page from the left menu.
Use the Search box to find the user - click on the desired user to open the settings page for that user.
Look for the Administrator access section on the page:
This will indicate if the user is an administrator - if the user has "...no system-wide access..." they are not an administrator.
If they "...are able to access and manage all users..." they are an Administrator.To promote/demote the user click the Change button.
You will now be able to select between two roles:
User: Select this to demote the user back to a normal user.
Administrator: Select this to promote the user to an Administrator.
If you demote a user...
They will only be able to see groups (and devices) they are added to. You should now click the Manage group access link to review the groups the user can see.
If you promote an Administrator...
They will now have access to all functions/settings and can see all groups and devices. The only additional setup required is if that user needs to receive notifications from devices (e.g. a motion detection event). To receive those the user should be added to the groups they are interested in - use the Manage group access link to review the groups that the user is in.