How do I upgrade my Dell Optiplex I-390 I3-2120 CPU

[Dp3102]

I would like to Upgrade my Dell I-390 computer to do more, game, youtube, multiple programs open at the same time, any advice would help. I have a Dell Optiplex DT 390 desk top Intel core I3-2120 CPU / 3.30 GHz, 4GB DDR ram, 64 bit dual core, 250watt power supply.
I would like to upgrade my CPU from dual to quad core, new graphics card and add 4 more gig off DDR ram. Where do I start? 😀

 

[JingLuci]

That CPU is a LGA 1155. So you'd got to find chipset of LGA1155.
Your options are the following. http://processors.specout.com/d/p/LGA-.-1155

I would suggest you getting a 8gb DDR3 RAM kit instead of buying another one ram and topping it off to 8gb. This will prevent any issue concerning compatibility.

Your PSU has to be upgraded to at least a 500W-600W.

Once all this are done then you can start looking at GPU options.