In SourceTree, how to go back to previous commit and delete new files?

Question

So before I upgraded a third party plugin in my project to their newest version, I did a commit so I could reverse the changes if things went haywire.  Well, things went haywire and I'd like to restore the project to the state it was at with the last commit.  I tried 'Reset master to this commit' but it seems to have kept some of the new files added when I upgraded the plugin even though I selected hard (discard local changes).  There's many files, so manually deleting the problem files would be tiresome (why I made sure to commit before upgrading).

Anything I can do in SourceTree?

edit: does removing files in SourceTree delete them?

Aseem Parikh_nrfvsl · Answer

Try the "stash" feature. Stashing (untracked files must be staged when using sourcetree, I believe) will leave you with a clean working copy up to your last commit. If you decide you want your changes back, you only need to apply the stash. If you want to discard your changes, you can just drop/delete the stash.

Justin Pierce · Answer

So I was able to browse Uncommitted Changes and delete the files that had been added.  Seems to have solved my problem, but I'll still give credit for the answer if someone provides a cleaner solution.