You can remove Test Runs from Milestones with a couple easy steps:
Choose which Test Runs to remove
On the Test Runs page of the Milestone you are working on, tick the check box next to the Test Plans you wish to remove from the "Selected" tab, and they will be automatically removed.
Select the Test Runs you want to remove
Next, let's take a look at how we can filter what Test Plans we want to add to our Milestone. Click "Next" to continue.