It is extremely easy to remove the old drivers. In fact I do it even if I upgrade from one nVidia card to another. Just uninstall the old drivers like any other program using the Add/Remove Programs tool and then download and run the program "Driver Sweeper" http://phyxion.net/item/driver-sweeper.html
Then just download and install the latest drivers from AMD. AMD has made up some ground in recent years on nVidia in GPU performance and generally they are neck and neck. I don't really prefer one to the other. My current card is the EVGA GTX 690 because it was such an incredibly engineered and designed card. Before that I had 3 Radeon HD 6970's in TriFire (Really a 6990+ 6970), and they performed great and scaled performance really well. But It was a loud and noisy setup. http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107.html
Here is the chart from Tom's that goes into detail on the best cards for the money. You'll see AMD dominates the list, mostly due to some incredible price cuts.