If in Admin > Classes your class names do not reflect your new groups you may need to update the groups via Admin > Config > Core Set Up > Groups.
In this area you can either add new groups in the abbreviation and description field, if the new groups match your registration groups you can click onto "Auto fill from form groups/pastoral groups" to copy these into this area or alternatively you can amend the names by clicking onto the edit button. If you choose to edit the groups this will change any existing assessment class names in Admin > Classes. If not, you may need to add new classes in this area.