Yes it is possible to upgrade ram up to 16gb. Usually it says this model comes with 2 RAM slots, but only one is used for 1x8GB ram stick.
You should open the laptop and check what model is the other ram, so you could get the same model RAM OR you could try to switch your 1x8 for 2x8 where you will pay the difference.
Also there is no ram compatibility info on Lenovo website, either get sticks and try em instantly OR call Lenovo before that, for a compatibility list.