Duplicate files - Please help

Hello there,
Please could somebody help me. I ran a download I got from this site which showed me all my duplicate files on the p.c. There were over 5,000 files which were duplicated as I have had the p.c. over 2 years and this is the first time I have heard of duplicated files.
The download did not tell me which files I should remove and said I had to be careful as some of the files and entries were needed to run my p.c. properly but lots were just duplicates.
I have not deleted any of the duplicates that were found as I do not know which I should get rid of and which I should keep as the site did not tell me it just said to be careful when running the programme.
Could somebody please tell me a site or programme to run which will tell me which duplicate files I can delete and how to do it so that I do not harm my p.c.
I have had a p.c. for a couple of years but I am just finding out about all the info on this site and I do not really understand the technical terms as it is way over my head.
Please could somebody help me as if I have over 5,000 duplicate files and things (I am not sure what) it must be slowing down my p.c. and I would like to get rid of them but I am not sure which to remove so I do not harm my p.c.
Thanks for reading this and for helping me.

 

It's not that simple.

A lot of programs need and install duplicate files in different locations.

Removing any will break that program.