can you even upgrade a laptop!?

Very very limited, usually only SSD's as laptops have soldered parts.

To OP, as others have said, building is the  best way to go. You can build a decent rig for 500-650 bucks that'll out perform any prebuilt store PC. If you are willing to do that, that's the best way. If you are really on a budget, depending on your specs, you can pick up a GTX750Ti or R9 270X that'll run GTA V decently but as mentioned before, depends on the other specs you have.

Originally I got an Asus Laptop from BestBuy for about $860 but it wouldn't play GTA V well. The guy there told me about the Alienware Alpha and recommended an i5 or i7 for GTA V but said the i3 with at least 8GB of RAM "should" work on low-med settings. My issue was FPS, but now I have no issues (Mod crashes aside, grrr! lol). The AW i3 is really nice. IMO.

Alienware is way overpriced. Literally the Apple version of PC gaming xD

Alienware is way overpriced. Literally the Apple version of PC gaming xD

That's what I hear all the time and it may be true. The Alienware Alpha i3 that I purchased is around the same price many suggest spending on building a PC or far less than gaming Laptops. So for that price, I don't have to build anything (only upgrade RAM which was simple). I'm certain building one would be more powerful but that's not something I'm too worried about nor want/know how to do myself.

I was jut sharing my AWAi3 experience for others who may be interested or dig the whole console look of the AWA systems. I wanted something to fit with my PS4 and XBOX One and to use on my TV. If asked, I'd recommend an i5 or i7 but the i3 works.