Working with PC hardware is easy - think of it as big overpriced puzzle
If you have normal PC (not notebook) all you need to do is check specs of your PC (should be available online somewhere) to get info about your motherboard (to make sure your GPU use PCi-E or AGP interface), power supply (to make sure that your PSU can provide enough power to your new GPU) and graphics card and based on that info you can easily pick new GPU and after that just powed down PC, open case, pull original GPU and replace it with new one. There are lots of guides written about this on www - just google it.
Of course its much easier for people like me because PC hardware is my hobby so if I were to get xxx to get new GPU, it would take me 10 seconds to choose which GPU, another 30 seconds to order it from my supplier and when it arrive next day it would take me about 2 minutes to switch them.
So best advice is that if you are affraid to do it even after doing some basic research via google and you know someone (friend, relative etc.) who is good with computers, ask him to help you with it and to explain what, why etc. - next time you will be easily able to do it on your own.
If you are interested check forums and ask there if you need advice:
http://hardforum.com/
http://forums.anandtech.com/
thanks for your help
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