|You need 64-bit Windows if you want to install more than 4GB RAM.|
If you have 32-bit Windows, the usable limit is 4GB installed RAM, (though it will show as only 3.2GB usable or something near that figure in Windows, but that's still better than what you currently have).
More RAM will certainly allow your laptop to run faster, but remember what the limit is for 32-bit Windows. It can only use between 3 and 4GB. You can install 8GB but half of it won't get used at all, so you would have wasted your money.