This problem is referred to as color to color alignment. Most color laser systems have a rough adjustment by means of a screw somewhere and a fine adjustment that is done in diagnostic mode as part of a setup routine. Try the latter first by locating your manual and looking through the troubleshooting guide which should explain how to force the machine to do an automatic color alignment. Your manual should be available online from your manufacturer's web site if you can't locate it. If this doesn't work you will need to take it in for servicing unless you are handy with tools and can find a service guide for your model.