You can archive your screener but cannot delete it completely. To do this, go to your screener dashboard (Screeners>>Overview) and click "archive." This will remove that particular screener from the screener overview. You can always bring back an archived screener by clicking on "Restore Archived Screeners" and selecting the screener that you want unarchived.
If you are archiving a screener, be sure to take the ethnio code off of any sites! Otherwise you'll still be incurring pageviews.
Note that if you get an error that says you can't archive an active screener, you probably have it turned on still. If you still get that error after turning it off and on, try logging out and back in, and that should fix the problem.