In order to remove a pupil from a class you will need to go to Pupils – Groups – Select the relevant

Group Type:

Select a Group for example:

Click on it to open (this will allow you to see the members of the group (pupils is the default but you can click Users to see other group members)

Click on the Picker +/-

This will open up into a screen allowing you to select group members whom you wish to remove from the group:

Make your selection the screen will then show the following:

Click on the arrow (pointing to the right) to continue, and this will remove the group member.