I'd like to help you answer that, but that depends on two things. Do you want to build your own? Or buy a pre-made gaming rig from a company like Alienware, Xidax, or Origin? Either way, this will not be a hard task for you at all. Your current laptop can sell for easily around $2,000.00 give or take a hundred bucks or so.
If you take the route of buying a rig, I'd estimate that you'd probably break even on your sale of your laptop. If you build one, I can see you having enough left for peripherals, and possibly a few new games. I can better help if you decide what path you want to take. Either way, Id' start with backing up anything you want off your laptop, reformat it to factory state, and post it for sale.