First you'd need to determine what RAM your notebook currently has, and how many slots are occupied, one or two. For example
CPU-Z can show that information. If it's only equipped with one 8 GB module, it would make sense to upgrade the RAM, because then you'd add another identical 8 GB module for 16 GB total and Bob's your uncle. However, should it already have 2x 8 GB installed, then not only is that already enough for 99.9% of all games out there, it would also complicate the upgrading. Because ideally you want to have two identical modules, so you'd have to replace the existing 2x 8 GB with 2x 16 GB of similar spec (which would not really give you any advantage for gaming).
Anything that would be worth upgrading in a PC, like the graphics card, isn't upgradeable in a notebook, which is why i don't usually recommend gaming notebooks to people. You're stuck with whatever CPU and GPU are in there, and we know that especially the GPUs are things worth upgrading after a couple of years if you're a gamer, but you'd need a PC to be able do that. Upgrading the RAM will not give you a performance boost for gaming at all, it's perhaps the least effective upgrade for that, i'm afraid.
Also see
RAM explained: Why two modules are better than four / single- vs. dual-rank / stability testing, under 3) i explain why games don't really need more than 16 GB. Of course that thread is more about desktop motherboards, not notebooks, but a lot of it is generally valid.
