Issues with your group? Leave!
Update: The new groups are now formed, you cannot leave old groups anymore.
It seems that there are some cases where group members don't work together, e.g., one person does everything and the others don't react. If you are not happy with other group members, you can "vote against" them (if there are enough "negative" votes, this person will be removed from the group for the next exercise). You may also select to leave your current group on your own, then you will be placed in a new group for the next exercise. Of course, everyone keeps their points, even when changing their groups.