Just looking for General Upgrades (Budget Gaming)

Here's my current build I built about 4-5 years ago;

Intel G860 Asus P8B75-M (1155) 4GB DDR3 AMD Radeon HD 7800 550w PSU

Games I usually play aren't too graphically intensive (LoL, HoTS, WoW, D3) so I want to easily max those and I would like to game at medium levels for more graphically demanding games (30-60fps).

Wouldn't mind upgrading parts here and there just to have a better overall PC.

I live in Canada and just to ballpark a budget I would say $500. I would like to get the parts in order of what would help my PC improve the most.