having just bought a new car it has a monitor with a touch screen and an operators manual of instructions[50pages] all i want is a cd/mp3player and radio.anybody know if you can take it out and replace it with a system that my brain can understand

Best option is to find a teenager and ask them to show you how to drive the touch screen. You may find the basic functions are not as bad as the 50 pages suggest.

I doubt changing to a simpler audio system would be a good idea but your options will depend on you car. Simple audio systems are becoming rare and usually are cheaper single DIN size units. Most cars now have the audio systems integrated into the fascia. Changing from the 2DIN DVD to a simpler system would probably need a suitable after market system and fascia adapter panel, (if one is available).

Your car may have a cheaper model variant with a simpler stereo that could be used. Car manufacturers are not known for competitive pricing for this stuff though.