You can view all the groups to which a user belongs on Users > Local Users & Groups. Click on the Expand icon next to a user to view the group memberships for that user.
The columns to the right of the user’s name list the privileges that the user has. In the expanded view, it displays which group the user gets each privilege from.
To:
Remove the user from a group, in the expanded view, click the Remove icon in the user’s Configure column.
If the user cannot be deleted from a group, the icon is dimmed.
Delete the user or group in that row, click the Delete icon in the user’s Configure column.
If the local user cannot be deleted from a group, the icon is dimmed.
The bottom of the Users > Local Users & Groups page displays the total number of local users: