You need to use an image editing program like Photoshop to make several small images that will fit together to make up the larger image. Photoshop has a 'slice' feature that can do exactly that. But more likely your image is larger than you need it anyway, so perhaps try resizing it in your image editing application first to make it smaller. Yes, it definitely improves performance, the more 'big' images you have, the longer it takes to load the game, the more memory it uses up and the slower it runs (potentially). Keep your images small, and think of ways to reuse the same images for different purposes, look at the way almost every game that exists (except for some strong art games like Machinarium) use 'tiles' to create their levels, reusing the same tile over and over.