How can I add or remove group leaders?

If you are a group owner, click on the "Members" tab in the group and search for the person you want to add or remove as a group leader from the group.

Once you find them click on the "moderate ∨" button next to them. From that dropdown menu you can choose "Add as Group Leader" or "Remove as Group Leader".

Note: only one member can be a group owner, but you can have many group leaders. A member on the pre-moderation list can't be made a group leader until they're removed from the list.