Laptops usually includes the max amount of RAMs it can be upgraded with. For starters, what's the model number of your notebook? For typical use, 4GB of total RAM would be sufficient. Although more won't hurt. :P
The point is, what's your definition of poor performance? If you compare it to similar spec'd desktop PC, of course the performance is not as high. The power requirement itself is greatly different, which is why you can't expect to have the same performance from similarly technical spec'd desktop PC.
If you're certain that it's because of insufficient RAM, then your plan of upgrading it is appropriate.