Check the other topic in this forum (http://techtablets.com/forum/topic/x2pro/) – the poster Rahul has kindly already posted a whole bunch of internal photos.
I myself did the upgrade. Its very easy.
The case opens with just clips (i used a guitar pick to pry the edges open), the original SSD is exposed and requires one screw to be removed (under some tape). Insert the new one and its ready to go! Before you do anything, make sure you take a driver backup.