Are you a IT technician by any chance? if so I can help you pick out a RAM module, however it's not really a task for a novice user. It's quite hard to do RAM upgrades on any laptop, let alone the sleekbook which is extremely thin and compact/crammed. You'd most likely have to pull apart the entire laptop.
I honestly wouldn't recommend it unless you have prior experience. Sorry for the bad news.
As for RAM, anything in DDR3L-1600-MHz area is fine.