Before upgrading Ram, look to see in your system where the bottleneck is. Get into task manager or resource manager and see how much memory is being used, and how much you have available. If you have less than ~20% of memory available in your system, then it is time to upgrade.
Typically high end games will eat up ~5GB of ram in total. This means that 4GB is really not enough, but 8GB is effectively overkill, and 16GB is really unnecessary (for now at least). But if your system has a lot of background processes, or you are a very heavy multi-tasker, then moving up to 16GB of ram would be a good call.
For a real world example:
My wife's PC has 4GB of ram, and typical usage is 1.2GB idle, or 2-3GB when working (office and web).
My PC has 16GB of ram, idle is 2GB (too many background processes), web and office 3GB, gaming is ~4-6GB, and video editing (what it was made for) is 12-20GB and it eats into virtural memory a bit, which sits on my SSD so it is not exactly a crippling issue like it use to be when I had a HDD.
Again, check and see if the other system need the memory. System memory makes a night and day difference if you are out of it, but if you have even slightly more memory than is needed, then it makes little to no difference at all.