First get Speccy (nice, simple and free) and use it to find out what kind of ram you have (clocks, timings and voltage). Then after you have done that find out if you even have any free space to install more ram (there should be a section or two that you can remove on the bottom of your laptop).
If you have more space just get the same ram (at least the same specs) and install it, otherwise get rid of the old ram and get some good new ram /
It should look something like this (yes, I haven't got my MSI x360 yet fags and yes, my CPU can do 2+GHz and yes, I have another gpu but i'm on power saving):
There you can see that I have DDR3 ram (you will probs have DDR2), the next number (533MHz) is the frequency (mine is half the real one, it's just like that, I won't explain how this works now) and the last set of numbers is the timing (7-7-7-20).