How do I add/remove a user to a usergroup?

There are two icons next to the groups. Use the two figures icon to add users to a group.

The tab "Assigned" lists all users assigned to that group. In front of the assigned user is a checkbox, there can be selected for one or more users to be able to and move them to tab 'Unallocated' using the button "Remove from this group'.

The tab "Unassigned" lists all users who are not assigned to the group. There also have checkboxes in front of the users. By selecting one or more users in the same way as described above, users can be assigned to the group using the 'Assign to this group' button.