Yasir. this is not a task for the DIY'er that does not have the right equipment. The quad-core processor is a BGA chip. To exchange a BGA IC you will need to have special equipment, like a reflow station as well as the right solder balls and the proper stencil for the solder balls. If you do not have those tools or have never done this, there is no way to do it right the first time. You most likely will also have additional problems obtaining a replacement processor. Those are not easy to come by as well. I suggest to try and find a replacement logicboard or replace the phone. Some repairs are just not feasible for the DIY'er