If you have the money, do some research (very hit & miss) and then try some new cables. Morrow Audio makes some very nice sounding cables, and many of their lines are competitively priced.
The key with system changes like this is to replace all of the cables in your signal path (or at least your most important signal path) and then just listen to music over time. Don't try hard to hear any immediate differences. If you do, fine, but you'll still want to live with them for a least a month-- over time you'll develop an opinion of what, if any, changes you're hearing-- after listening to lots of music, hopefully all of the kinds you normally listen to (and are familiar with).
Sometimes the change IS better, but probably, most often, you're not hearing "better" you are hearing "different". You decide if those differences are better, or are just subtle trade-offs that don't matter much to you. Unless the cables you're replacing are damaged, or are complete crap, you should expect some differences. Beyond that, it's up to you to decide if those differences add up to a real improvement that you feel is worth it. Or not.
What is for certain true is that, above a certain level of build and materials, more money does not equal more quality. Period. Fact. It depends upon your ears and your particular system AND your room.