To change a group member to a group manager or a group manager to a group member. Go to the group management page for members as shown below.
1) look at “all members”
2) select the members whose role you want to change
3) from the “Actions” drop down select “add to role”
4) click on the “role” you want the member to change to. Normally that will be either “member” or “manager”. If you are an “owner” you can promote someone else to “owner” but remember owners are the only ones who can remove a group altogether.