I have a intel I5 with HD 4600 graphics and I use that to play games and I have 4gb ram. Should I first buy ram or buy a new dedicated graphics card like the geforce gtx 750ti 2gb.
I'd go with the graphics card. Depending on how many background programs are running, you could safely run just about any game with only 4GB of RAM installed.
First Priority is for the GPU, go fo the graphic card. After that buy the RAM in coming time. Because upcoming games needs minimum 6GB ram but still they can run on minimum settings with 4GB ram.
Go with Graphics Card. As the Graphics Cards have their own VRAM so it would come handy. Make sure to buy minimum 2GB VRAM graphics card. Also, are you limited by budget? Why 750Ti?
You should definitely get a GPU first, then get the RAM. You should be fine with 4gb RAM for now, as my friend has 3gb of RAM and he can play pretty much anything ( he closes all the unnecessary stuff running in the background e.g Antivirus etc ). I would recommend you upgrade the RAM as soon as possible, but get the GPU first.