The best way to reinstall iRacing is to first remove it from your Windows Control Panel...Add/Remove Programs. 




Then delete the C:\Program Files (x86)\iRacing folder.



Empty your Recycle Bin.


Then reboot your computer.


After that, access http://members.iracing.com and follow the download/install/update instructions.


You can find more details in this FAQ: https://support.iracing.com/en/support/solutions/articles/31000133472-how-do-i-download-and-install-the-iracing-software- 


Although your setups and replays should not be affected in this process, if you feel more comfortable, you can first back up your Documents/iRacing/Setups and Replay folders first.


To save time (and bandwidth), you can back up your C:\Program Files (x86))\iRacing\Cars and Tracks folders to another location.


Then after deleting and reinstalling the iRacing program, before doing the download/updates - replace the new Cars and Tracks folders with the original ones. Then go back to the iRacing Members site and click Refresh. You may still need to do a small update but it will be much quicker.