Hummingbird minified files

I'm having trouble with the Hummingbird plugin. I've noticed on one of my client sites (not sure if this is happening on all sites), hummingbird when minifying files, has created thousands of files over the past few months for css and js and doesn't delete them after it stops using them.

So I'm trying to delete them now via SFTP, which is taking forever, but I just don't want it to happen again or was wondering if maybe there's a way to delete them via the plugin interface.