A User can be removed from User Groups through the Web Portal > Admin > All Users > Edit arrow for the User that you would like to make the changes to > deselect the User group/s that you don't want them to have access to > scroll down and Save.
This can also be done through the individual group on the Web Portal > Admin > User Groups > Edit arrow for the group that you would like to make the change on > deselect the User/s that you don't want to be in the group > Save.
