Make sure the group is empty(if you dont want to delete the parts in the group), and then click on the group in the list and press delete, this works for me!
Another way is to select the group in the list and press ATL+J, or click the ungroup icon in the left side bar. This way the parts are not deleted even if they are still in the group.

The remove option is to remove parts from the group, to do this, select the parts you don't want in the group and the click remove. Same as Add function but the other way... 😃