There is more to getting a new graphics card than just getting it. Depending on your current computer specifications, you may need to upgrade your power supply. Additionally, your current hardware will limit how far you can upgrade. If you get a graphics card too powerful, it will bottleneck your CPU. If you upgrade your CPU, you'll probably have to get a new compatible motherboard as well, and then the PSU....
Basically, you should tell us your computer's specifications so we can give you a recommendation.