C drive full and I'm not sure what files to safely delete.

My C drive is showing up as FULL. I had this issue about 6 months or so ago and took the computer to my local computer store. One of the techs downloaded WinDirStat which unearthed a weird log file that was voraciously gobbling up all the space in the C drive. (Sorry, I don’t know the name of the log file.) The tech was able to remove these nasty files and everything was great! Unfortunately, WinDirStat got deleted from my computer somewhere between then and now (my bad) and NOW I can’t download it again because the C drive is full! Can someone help me figure out what files I can safely remove to resolve this issue (from the comfort of my office rather than at the computer store?) I can share a list or take a screen shot of the gigantic files if that helps. Thanks in advance!