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You've got a couple of options depending on your budget.
From Nvidia I'd be looking at a 6GB GTX 1060 at about £250 or so or a GTX 1050Ti if you want something a little less expensive.
If you want to stick with AMD then either the RX 570 or RX 580.
Just check the prices and see what fits your budget.
GTX 1060 3GB for £180 on this very website.
It’s all in the OPWe need to assertain which model graphics card he has, those cards recommendations could be at best a side grade, maybe even a downgrade from what he has now..
Any r7 200 series has much lower performance than a 1060 3GB.
It’s all in the OP
Will these cards fit the socket on my motherboard? I read something about finding a graphic card which will fit the socket?
I don't know much with pc's sorry.