Please note that all Groups must have at least one moderator at all times. In order to ensure this, there is the concept of the "Primary Moderator". If you are trying to remove a moderator of a Group and that person is currently the only moderator, you must add another moderator first.
Instructions for adding a new moderator are here:
To remove someone as a moderator of a Group:
1. First go to the Group Home Page.
2. Select View All underneath the list of people.
3. Find the person who you want to remove as moderator.
4. Select 'membership & settings' under their name.
5. On this next screen you can change their role in this Group.
5a. If they are currently the Primary Moderator, you must first choose one of the other moderators of this Group from the drop-down menu under "Assign new Primary Moderator", check the box next to "Click here to confirm assignment", Save, and then return to this page to perform step 5b.
5b. Assuming they are not the Primary Moderator, you can change their Role in this Group to "Member" or "None. Remove from this group."