Once the keyboard is carefully removed and the cable disconnected, the system will look like this. You can find the single memory socket for system ram located to the left and the twin cooling fans in the center / right of the system.
Next, remove the palmrest assembly - there are a number of small screws located on this metal plate which secure it, along with clips at the perimeter. Be careful to disconnect display, battery, and touchpad connections as necessary, referring to the instructions in the hardware maintenance manual.
Tip: If the fans have any accumulated dust build up, this is a great time clean them with canned air.
The factory 128GB mSATA SSD is located in position 1 shown in the picture above, while position 2 is the empty slot for a second mSATA SSD.
Here is a closer view of the empty slot for the second drive. Note the retention screw hole in the upper left corner - no screw is included from the factory. A local hardware store may be a good source - you can borrow the one from the factory drive to take along to match length and thread pitch.