How do I update my AMD Radeon HD 6770m Graphics Card Driver?

Right now I am trying to figure out how to update my graphics card. From what I have gathered it seems like you need to use bootcamp and purchase a Microsoft platform to do this. Is there any other way to do this without buying Windows?

I have a late 15 inch 2011 Macbook Pro with these specs:

Processor 2.4 GHz Intel Core i7

Memory 8 GB 1333 MHz DDR3

Graphics AMD Radeon HD 6770M 1024 MB

and I am currently running lion.

Any help would be appreciated 🙂