Looking for advice in selling 4.5 yr old Alienware Aurora Alx

Hello all, 

Just to start off I don't have much experience with PCs, computer hardware, etc. I plan on doing a lot of research before I make any final decisions about my desktop but my plan is to sell it and look for a laptop. I appreciate all advice.

I have an Alienware Aurora Alx desktop (Late 2011) with an Intel core i7 cpu, 920 @ 267 GHz, 6 GB of installed RAM. I have 2 AMD Radeon HD 5670 gpus connected with AMD crossfire.

I run a ton of different games on it at the highest graphics settings with no problems, Civ 5, LoL, Cities: Skylines, CS:GO, Dota 2, Arma 2, and Rocket League to name a few.

Im just looking for advice about range of price, where to sell, how to find buyers, etc. Any help is welcome and appreciated. Thanks for taking the time.