Board Thread:General Discussion/@comment-26330800-20150827230958/@comment-4018164-20150827231815

This is done via Special:Userrights, where you can mark the groups that you'd like to add, and unmark the groups that you'd like to remove. The easiest way to do that is by going to someone's contributions page, and click the "user rights management" link at the top. This will lead you to the user rights management page for that certain user.

Just note that when giving someone bureaucrat rights, you will not be able to remove them- so be careful when handling this group.