RAM does nothing for games except for load times (starting the game and loading save games). It slows you down if you barely have enough to run Windows properly, but won't speed the game up (add frames per second) if you aready have enough RAM, which you did with 2GB. 2GB is fine on anything but Vista. While 4GB+ is better than 2GB on Windows 7 64 bit, it still isn't so bad that its slows games down. Maybe if you were playing Skyrim with the HD texture pack, but not Runescape.
I'm guessing the problem you have is
1) your laptop probably has a slow integrated graphics chip, like an Intel GMA or HD. That can't be changed or improved. You have to buy a laptop with a decent dedicated graphics card built in from the start, or you be forever limited on gaming. There is videos on youtube showing Intel GMAs running Runescape very choppy, so this is likely the case
2) If you have a decent graphics chipset, then it could be an Antivirus programs slowing you down. Kaspersky Pure, Norton Internet Security, and some others slow down machines quite a bit
or
3) Don't run on battery and make sure your power profile is set to High Performance, so your CPU isn't slowed by Windows to save power.