Steam Problem: Unable to delete local content

http://support.steampowered.com/cgi-bin/steampowered.cfg/php/enduser/std_adp.php?p_faqid=62

Ordinarily you delete local content (the cached files) by right-clicking on the game in your games list in Steam, selecting "Properties," and then clicking "Delete local game content."

If you find that this is not working, you will need to exit from Steam and then delete the GCF file(s) manually.

These files are usually located here:

C:\Program Files\Steam\SteamApps

Once the file is deleted, you will need to re-download the content in order to play the game again. This will happen when you click on the game in your Games menu.

You may need to wait until the download is finished before you can play.