Visit the user's profile, and under their "contributions" tab, you will see a link that says "user rights management". That's where you can add/remove certain usergroups for each user. This can also be done by visiting Special:UserRights on your wiki.
Hey there! Please edit the title of your post and make it more specific. Titles such as 'Help' or "I have a question" give others no indication of what might be going on. This is also mentioned in our discussions guidelines, which I recommend reading before contributing to any wiki. Thanks!
Since you ignored it, I added the topic of this post to the title, a title like "hello", "help", or "a question" doesn't help others understand what you are talking about, and asking a question or introducing a topic at a first impression makes it that little bit easier for people trying to help. This (and other recommendations and advice) is also stated in our discussions guidelines.