Go to C:\programfiles\electronicarts\crytek\crysiswarhead

Dump all that to the recycle bin.

Then go to C:\users\documents\mygames\crysiswarhead

Dump all that to the recycle bin. Then empty your recycle bin.

I advise you try using CCleaner to uninstall Crysis Warhead properly before you manually delete the files, since I am not sure if it will make it reinstall properly by just removing the files and not using a program to do it.

Run some cleaners like CCleaner to scan and fix your registry. If that doesn't work (be careful!) go to Run and type in the box : regedit and Enter.
Be sure that you minimize in there and select the top one. Press CTRL F to search for "Electronic Arts". With F3 you can search for 'next' and always check where you delete the line. If you aren't sure, you can use 'export' to have the 'reg' as backup purposes.

Warning: you can fix and detroy with "regedit" as it is a leading asset of Windows and the core HAL layer.

#Note: I hope you used the 'de-autorize tool' as you can re-install Warhead 5 times.