DDR3L 1600 MHz SDRAM, 1 x DIMM socket for expansion up to 8 GB SDRAM
up to. That means that you can add another 4GiB SoDIMM (type DDR3L @800MHz) in order to get 8GiB useable memory. See @Jonno's post for more details.
You might be able to add more, but if a manufacturer claims up to X GiB than that either means:
- That that really is the max (e.g. due to chipset limitations, max width of copper traces to the DIMM socket etc etc),
- or that that only tested it with memory up to that much memory. E.g. because that was most which was available at the time the manual was written.
And also I have a spare 2GB RAMDDR3 Module @ 1333MHz.
Can I use this? What will happen if I do?
You might be able to use it. DDR3 memeory works by default at 1.5v. However DDR3L also needs to be able to work at 1.35 volt. (The L is for lower voltage).
What probabby will happen is that both old and new memory get 1.5volt. Both should be able to work with that. Both will be clocked at 667MHz (which marketing writes as 1333MHz since it has two accesses per cycle). And you will have 6Gib useable memory.
All this assumes that the CPU will also work with the higher voltage.
http://ark.intel.com/compare/84697,85212,85214 shows that at least three models of CPU's used for your model of laptop are not designed for anything but DDR3L though. Which might not mean anything. People reguarly feed more power to the memory and the on CPU die memory controller to archieve higher speeds and most of the time it tends to work. As for this specific model or these CPUs: I have no personal experience with these. I would add a secondf SoDIMM with the same specs as already on the laptop since that will guarantee 8GiB usueable and 8GiB is usually enough for a laptop. If you need more go to a shop and ask for a larger SoDIMM and for the shop to test if it works before they make the sale.
Recap: It probably will work.
Note that memory access will be slightly slower, but more memory usually trumps slower memory.