Alright, I know what this guy was trying to say.
1) Open Steam\steamapps\common\call of duty modern warfare 2\players
2) Delete all STAT files.
3) Open up Steam\userdata
4) Now, while in this folder, do a search for a folder named "10190"
5) 1 Result should come up
6) Open that folder
7) Open Folder named "Remote"
8) Delete both files in folder
9) Start up Call of Duty: Modern Warfare 2
10) Congratulations, all player stats should be reset ( Including Rank )