Okay, I'm following Badspot's tutorial to update it, but they don't have ATI Radeon 4850; it only goes to 4800.
As you can see, I have a ATI Radeon HD 4850 model. On the website, however, the highest model they have is the 4800 model.
The 4800 driver is for every card that starts with 48XX, Such as the 4850, 4870, ect. Download that one.