I don't think that laptop has MXM graphics card so you cannot swap it out.
You have two option:
1. vidock if you have expresscard slot or 2. you can open the computer and use the mini pcie connector, connect mini pcie connector to pcie x16 converter and a desktop psu for power. But I don't think you want to do number 2 because you have no mobility at all. Either way, your graphics card will be very bottlenecked by the bandwidth and they cost money.
The price of vidock combined with a decent card like a 6670 and you can almost get yourself a game ready laptop or a desktop.
So it is better to sell the current one and combine with that $300-400 upgrade for vidock and gpu to get a a desktop gaming build or a gaming laptop if you need mobile gaming.