Deleting duplicate files

[Clint]

I recently downloaded McAfee Quickclean Lite for a free
trial. It shows that I have tons of duplicate files from
downloads. There are duplicates to Administrator,
Default User, my log-in name, and C:\1386. These
duplicates are taking up a lot of disk space. How do I
know which ones to delete, without deleting something
important? I'm kind of new at all this.
Thanks for any help or advice.
Clint