Instructions
Search the Internet for Multi Theft Auto modification software, such as MTA Map Editor, MTA Race or TXD Workshop.
Download the modification software onto the computer.
Run the modification software. Open a game save file from Multi Theft Auto to use as a template for your mod.
Use the modification tools to alter the Multi Theft Auto in whatever fashion you desire. For example, if you use MTA Map Editor, you can change the height of buildings, the locations of quest objects, the direction of traffic or even move bridges.
Save your modifications to your computer, creating a new game save file. Move the game save file to the ̶0;Game Saves̶1; folder in the Multi Theft Auto folder of your computer.
Run Multi Theft Auto.
Select the modded game save file to access your modded game world.