Synced a bunch of files from someone else's account and now i can't get rid of them

I had to use a colleagues account once and it automatically synced 200gb of files that I didn't want. I logged off his account and now apparently the files are hidden somewhere but its still taking up 200gb of space. I don't want to have to log in to his account again. How can I delete this stuff off my computer while making sure I'm not deleting anything remotely for him?