I doubt it's possible as it will be a different socket/chipset - if you had a desktop PC with a 4790 you'd need a new motherboard, and for a laptop the motherboard is basically the whole laptop.
If it's any consolation it's not really worth the upgrade:
http://www.anandtech.com/bench/product/1199?vs=1542
Indeed. http://ark.intel.com/compare/88195,88196,80807,80806
(scroll down to Sockets Supported under the Package Specifications section)
so I cannot upgrade at all? half the reason I purchased this laptop was advice from the sales team and being assured the MXM would make this upgradeable to skylake and future gpu's