Lets say I did a check out, edited some stuff and realized I want to re-download the repository code and overwrite my local changes without commiting them.
I downloaded
You can either revert the changes (right-click, it's an option) or you can delete the file(s) in question and update. The difference is, revert will revert to the last version you checked out, while delete and update will "revert" to the latest version in the repository, depends on what you're trying to accomplish. Oh, and revert can be done w/out access to the repository, where delete and update can't.
Andy adds a good point that a diff is in order to make sure you're discarding what you think you're discarding. Many times I've forgotten about changes I've made and blew away more than I thought I was.