First of all I would like to point out that maximum RAM you can install inside this netbook is 2GB. But before you try to by new RAM in your favorite store, please have a look at the support article below. There is a problem with compatibility of memory modules. For 2GB memory modules there are only 2 of them which are listed by Lenovo as working.
To get more information about memory compatibility, look at the following article: DDR2 and DDR3 memory types on S10-3 IdeaPad
I have just ordered Hynix memory module. I will inform you in comment about the success.