Should I change my CPU if I want to change my graphics card?

You need to make sure your motherboard supports the DDR3 in the graphics card, otherwise it would be a waste of money. You do not need to change your Processor (CPU) but again, you must make sure they work well together. The information is usually available on the manufactures website. You also need to check you laptop has a PCI express slot (lots don't) it can be quite hard to upgrade your laptop. Good luck!