laptops are different from desktop pcs. Many laptops come with specially customized parts that saves space and that often leaves no room for extra ram slots.
The laptop you mentioned is old, and use DDR2 ram. They are limited even further by density - so 1 stick usually only allows up to 2 GB ram. Even if you find a high density stick that has more (uncommon and very expensive), they may not fit inside the laptop at all.