GPU for Notebook

In most all cases the card is not replaceable because either it is part of the motherboard or because each card is different (there are no size/connector standards like a desktop). One exception is if your notebook could have a 4670 from the factory as an option. Then it may be possible, though you still have to find some way to get the card (they certainly aren't sold on Newegg).

Every now and then a GPU for an alienware laptop will show up on Ebay.

It is certainly possible to "upgrade" the GPU in a select few laptops, though most will have it built into the board, it won't be a slot card at all.

The tricky thing here is that any I have ever seen on e-bay sell for three or four times what an equivalent desktop part would go for. I get the impression the only folks that sell them are those replacing an 'old' laptop that is in some way broken enough not to be worth selling as a complete system... thus they are rare to find.

It is not a good idea to plan a laptop system around upgrade ability, if it is possible at all (would require a lot of research before you buy) it will cost a fortune.

The best upgrade path for a notebook computer is almost always a new notebook computer.

If you have a very high end gaming laptop there is a decent chance you have the ability to replace the GPU. If not it is highly unlikely. Even if possible a 4670 laptop 'card' will likely cost you more than 200 USD.