To remove a Related Case, head over to the Case Card, Details-view, under the Related Cases section.
Then hover your mouse cursor over the Case Name and you will see the Remove button appear as below.
Click on the Remove button.
The case will then be removed from the Related Cases list.
1. Ensure that you are either a Client Manager, Case Manager, or a User with 'Partner'-role, 'Assistant'-role or 'Administrator'-right.