The amount or type of ram you have installed in the motherboard is irrelevant to the graphics card.
What is your cpu?
How strong is your PSU?
Post a link to where you might shop since I have no idea how to convert your currency into relevant options.
Gta 4 is a CPU intensive game and maybe GTA V. So i recomend you to buy a quad core CPU (if you don't have one). But if you already have a quad core CPU you can buy a GPU like amd radeon hd 6670(the DDR5 version).