Doubts regarding RAM upgrade.

I don't have knowledge about RAM upgrade. A friend of mine is going to help me in changing those rams from the mbp.

Now. I have some doubts.

I have 4 to 5 tabs opened in Safari, Textual IRC app running and play WoW. These are three main apps running at the same time. I don't get any lags on Macbook Pro 15" Late 2011 with a 4GB RAM. But when I close WoW. There are small lags like, If I click Safari (which is minimized), it takes 2 sec to maximize or if I click ' CMD + T ' to open a new tab, it takes 2 secs to open. But after that the lag is gone. This kind of lag always appears when I quit the WoW game.

Also yesterday, my iTunes showed little lag when I was playing songs on full volume. I find this lag annoying because when it lags, the songs behave weird, like getting paused and start playing again. I hope you understand what I am trying to say about this iTune lag. This lag is only when I play songs on the macbook speakers. There is no lag when I use headphones with full volume but sometimes, headphones become uncomfortable (i.e ears sweat since I stay in a hot and humid climate) so I switch to speakers and then LAG and LAG ! 😟

Can I get rid of this lag after upgrading my RAM to 8GB ?