how to switch from CPU to GPU

I am new to blender. While rendering, blender sometimes crashes. I read a few reviews and they said that I should try to switch from CPU to GPU. How do I do this?

My system specifications are as follows:
intel core i7 processor 2 ghz
8 gb ram
AMD Radeon graphics card

Can you please help me?
Thanks
Mhk

That graphics card is not suitable for gpu rendering. You need a compatible NVidia card to enable CUDA
http://wiki.blender.org/index.php/Doc:2.6/Manual/Render/Cycles/GPU_Rendering