Instructions
Open the Windows Control Panel and click on "Programs." Highlight "Grand Theft Auto IV" and click "Uninstall" at the top of the window. When asked if you want to keep your saved games, choose "Yes."
Reinstall the game by inserting the game DVD and following the automatic prompts. When asked where to install the game, do not change the default settings. Installing the game on anything other than the primary hard drive can cause problems when running the game. If you have purchased the game from a download service such as Steam or Direct2Drive, log in to your user account on the game's website or desktop software. Search for "Grand Theft Auto IV." Select the option to re-download the game from the digital store's page for the game.
Download the newest patch for "Grand Theft Auto IV" (see Resources). Open the downloaded file and follow the on-screen instructions to patch your copy of the game to the latest version.