There’s lots of places that will sell the ram. I usually use Newegg, because I’m lazy and they have everything you need. I’ve bought bad ram before, going for the cheapest price, and having to return it. Find out the specs for your particular Mac , I think it’s ddr3-1600, still pretty cheap, compared to ddr4. The SSD is a generic part, but I always buy Samsung 860 evo, I’ve never had a problem with them, and they are the standard by what everyone measures against. I don’t know if you have an optical drive on that one, if so put a large capacity spinning drive kit into that, or just use a usb/FireWire/thunderbolt drive for files.
As far as how to do it, I could try and tell you, but YouTube is your friend on this one. I’m pretty savvy with this sort of thing, but I always review videos first. Secret tip, buy a usb to sata cable and Copy everything to the new drive first. Best $5 you’ll ever spend, they are a lifesaver! Also, make sure you have the right screwdriver to open the case. Apple sucks when it comes to This.....