Can I "boost" my HP Pavilion P6000 Series desktop?

Hello everyone! As you just read above, I would like to "boost" my tower so that I can play fairly well on current PC games? Here are the specifications: Windows 7 Home Premium (X64) Service Pack 1, Intel Core i5 2300 clocked at 2.80 GHz, motherboard: PEGATRON CORPORATION 2AB6 1.04, Chipset: North Bridge: Intel Sandy Bridge South Bridge: Intel H67, memory: North Bridge: 6 GB DDR3, graphics card: AMD Radeon HD 6450, hard drive: AMD Radeon HD 6450 and Intel Corporation 6 Series/C200 Series Chipset Family High Definition Audio Controller + Advanced Micro Devices, Inc. [AMD/ATI] Caicos HDMI Audio [Radeon HD 6400 Series .......... Well, I think I’ve included everything except the optical drive (hp CDDVDW TS-H653T). There you go!!! I'm looking for advice to boost it a bit (or a lot!) unless it costs more than buying a new one, of course..... I think I should start by changing the graphics card since mine is quickly becoming outdated!! So if someone here knows about this and could give me tips to make it more powerful, please let me know!!! Thanks in advance friends and best wishes!!!