Upgrading the Motherboard only

I would like to replace / upgrade my surface pro 4 “Motherboard Only” from the i5 4 gig ram to the i7 16 gig ram. I understand this is really hard but is it possible?

My surface is great and pretty much brand new I just can’t run anything on 4 gigs of ram. Used MOBO’s on EBay are under $200. A new tablet is well you guys know and I’m willing to take a “crack” at it ;)

Thank you ☺️