Removing a segment when creating a segment

Hey guys,

Another question about segments here (:

How do you remove certain users when creating a segment? For example, I created a segment that include 100 users who have been ACTIVE ON SITE. Now 30 of these users have also made a purchase and I want to exclude them from my segment. They already have there own segment called MADE PURCHASE but I dont know how to remove it,  is this possible? It seems im asking for something relatively easy but I can’t seem to find a way to do it.

Thanks