It sounds like your laptop is fairly old if that is all the amount of RAM it has got, I haven't seen any with less than 2 GB of RAM these days. It depends on exactly what you are doing with your laptop. If you are running games or graphics programs then you will need quite a lots of RAM, things will run very slowly if you haven't got it. However, if you are only using it for browsing the Internet or using Word for instance, then you might not benefit that much from upgrading to a lots more.
I have got a Fujitsu Siemens PC I bought in 2002 and it has only got 1 GB of RAM, actually, two 512 sticks the same as you, I only use it for browsing the Internet and it works perfectly okay, actually it's quite fast. But if I put some modern programs on it it would probably run a lot slower.