Only the account holder can grant administrative privileges. This is to help prevent over-propagation of administrative privileges.
If you're the account holder, click the People & Organizations link at the top of any page and make sure that you're on the People tab.
You can then choose any user who is a member of the primary company on the account (the first company on the page), just click on their name to go their profile page.
Head to the bottom of the user's profile page then select or de-select the "Administrator" checkbox. After that save your changes by clicking the "Update User Info" button and you're all set.
