Need upgrade help (New to PCs)

[MattCLewis]

Don't know where exactly I should be posting this, so I'm putting it here since I'm mostly looking at/for graphics cards. 

Bought a pre-built PC a while ago, (I KNOW, I'M SORRY) linked here. Apparently it runs a gigabyte ga-78lmt-usb3 r2 motherboard, an AMD FX-6300, and an AMD Radeon RX 560-B as best I can tell. I have a few questions so I'll just list em below.

1. When I upgrade this trash can, do I need to update my BIOS? If so, how, because google has been useless.
2. What should I upgrade to to improve gaming & streaming? Got about $750 to play with, was looking at a GTX 1070 but I'm pretty lost.Is GPU or CPU upgrade the way to go?
3. Would most AMD compatible graphics card work with this? Because I see that UserBenchmark says that they all are, but from best I can tell the RX 560-B is a cut-down version of the normal RX-560. Would there be a spacing issue even if I still have room in the case to mess with?

Anything else you guys can tell me about general advice or what I should be looking for would be really appreciated! Thanks and be gentle about the pre-built thing, I was broke and stupid.

[Herman Mcpootis]

I don't recommend upgrading to any FX CPU so you won't need an update for that, if you can wait, then you can get a zen2 CPU and B550 board.

[Inversion]

I'd say you should probably save for a bit longer and do a full platform and gpu upgrade. I'd suggest you wait for Ryzen 3000 and most likely pick up a new Ryzen 5 but wait for reviews. You'll need a new MOBO and RAM. That lot will most likely cost you about $400 to $500 in total. Then you can spend the rest of your budget on a new GPU, maybe a 1660Ti if you can't get a bit more budget and if you can maybe an RTX card or a used GTX 1080.