It looks like you have 8gb(2x4gb) right now. If you only have two memory slots and buy one 8gb stick, then you will have 12gb but in single channel mode. This may or may not be a bad idea, depending on what you use the computer for. Do you need 12gb system ram?
On the videocard, don't buy a DDR3 based card, or a DDR4 based card. On that website there's an Asus GT 730 DDR5 but it's out of stock. That would be the least I'd say you consider. There's a Gigabyte GT 1030 DDR5 at £82.55 which is probably what you should get in new cards at low cost. I realize that's more than the card you're looking at but here's the problem. What you're looking at isn't really much better than what you have. If you're going to spend money on a videocard then you should at least get something a bit higher in performance. If £60 is your limit, think about getting a used card. A GTX 750 Ti would be a much better choice.0