So, open handling.dat and find 'Infernus'.
In this example, we suppose that in the readme there is also these informations: Be sure that file isn't 'read only' (in properties). File is located \Grand Theft Auto IV\common\data folder. ChangeLogs- Version:v3.1 Recently Added: IVPack - GTA 4 vehicles in GTA-V 1.0. Handling.dat contains informations about vehicles. Added: 15:17:10 -0800 Replaces:More than 100 vehicles. To modify these files, you could use Notepad already installed on your PC. IMPORTANT: backup your original (or already modified) files, as we said in the GTA 4 modding introduction. Replaced by a total of 85 vehicles, modified vehicles, changed the settings. All these files are located in \Grand Theft Auto IV\common\data. GTA IV Real Cars ALL Cars Replacement PackDOWNLOAD LINK and CRASH TEST of all the cars. If in the readme there are information on handling.dat, vehicles.ide, carcols.dat or others, you must follow next steps. If there are information on handling.dat (or carcols.dat or similar files) follow next steps.