Sites such as and GTAGaming offer free downloadable mods for "Grand Theft Auto 4" for the personal computer. These mods offer new game features, such as textures, skins, weapons, vehicles and other upgrades to the game. Upgrades to the console platform versions are only available through paid downloadable content.

Gaming sites offer tools for managing and installing mods along with tips and tutorials for customizing the game. Players can add real-world vehicles to the game, such as the Ford Fiesta or Rolls-Royce Phantom, as well as fictional vehicles, such as the hovercraft from the film “Die Another Day.” Additionally, skins can update in-game weapons to look like other weapons, such as the M29 revolver magnum.