Because you only have Windows 7 32-bit I recommend a maximum of 4GB of RAM installed. Win 32-bit OSes can only recognize about 3.25GB - 3.5GB of physical RAM even if you install a total of 8GB, 16GB or more...
In order for the laptop (or any PC) to recognize the full 4GB of RAM (or more) you will need a 64-bit OS like Win 7 64-bit. I believe Win 7 64-bit can recognize up to 192GB of RAM.