How do i delete software from the list of softwares that i associated in "open with"?

In the later versions especially 7 Microsoft have not allowed any method of correcting this without actually changing the open with t another one. Typically short-sighted. And beware links to programs to fix this by third parties. Every one I have looked at is a spyware installer, relying on the high level access this change requires to push infections right into the system.