Alright, alot of people can't reset their stats cause it doesn't work or they can't find the "Reset stats" button in steam, so i will tell you how to do it :3:
1. Open up Team Fortress 2.
2. Open up the Developer Console (Be sure that you got it enabled in the advanced otions in the keyboard tab. If you can't open it up, type -console in the launch parameters)
3. Type: resetplayerstats
EDIT: Damn i posted it in the wrong forum... Oh well, i guess it is a Valve Game...