Shonabby.. the card is definitely upgradeable.. please refer to the Dell XPS One 2710 Manual page 69 for instructions (VERY EASY TASK). So you can easily upgrade to a 5Ghz Mini Card. Advance N 6235 is a good choice but not sure the Intel Widi will work with NVIDIA M640 though.. but you do get Wireless A,B,G, N (2.4 and 5 Ghz for N) + BT 4.0 EDR and Widi. (look it up and make sure it has the specs you want before you buy it) This is a 1/2 hour upgrade.. just make sure you completely remove ALL the drivers for your existing Wireless card before you crack open your case and replace it. You will also need to install all the drivers / software for the N6235 after it boots up. So go get the drivers before you start unless you also have a wired network set up to your dell as well. (suggest you download all the Drivers for the new Card before you start and place them on your desktop for easy access after you've done the hardware upgrade part.).
Caveat - this N6235 card is picky on the order the drivers are installed.. make sure you go to Intel's site and read the instructions they give the order of the Driver install you should follow.
Hope this helps.