Can't be done on that model, I'm afraid. Usually they're either the wrong type of socket or soldered in place. The removeable CPUs I see regularly are on the underside of the motherboad to make it hard to remove.
Dell wouldn't sell many of the high-end model range if upgrading the lower-end was an option.
You would need to be a very experienced hand with a soldering iron to take the job on. The worst part will be the de-soldering, in my experience. There's not much space between soldered joints in a laptop and you have only to partially melt one too many and you're in trouble.