It has 2 slots and one 8 GB module installed so you can easily upgrade to 16 GB by adding another 8 GB module.
The problem is that you'll have to peel off both long rubber "feet" in order to access the screws underneath, remove the screws then carefully "crack open" the case.
I've been considering doing this but in reality the 8 GB RAM is fine for basic computing.
Don't think there is space for anything else in the case since it is very thin. I use a high speed USB 3.1 flash drive for additional local storage.