re-install mw3

how to re-install cod mw3 on my steam? and if i do this i will reset my stats on the game?

Partial re-install:
Open Steam > Library. Right-click on Call of Duty: Modern Warfare 3 and click Properties. Click on Local Files and then Verify Integrity of Game Cache. This will check the files for anything out of the ordinary and will re-download them if necessary.

Complete re-install:
Open Steam > Library. Click on the arrow next to All Games and click Tools. Right-click on Call of Duty: Modern Warfare 3 - Dedicated Server and click Delete Local Content. Click on the arrow again and click All Games. Right-click on Call of Duty: Modern Warfare 3 and click Delete Local Content. After that, right-click on the game and click Install Game (download via internet) or insert the game disk and install again.

Doing both of these will not reset your stats, I've done it before.