Toshiba Satellite L25S119 upgrade/heat sink help

I have a Toshiba Satellite L25S119 - OS XP which I want to upgrade - it gets heated if not on a cool mat and once shut off.

Someone suggested replace the heat sink.

I now has 4GB RAM.

While I am replacing the heat sink what else can I do to make it more useful while I am there.

I only use it from web surfing and word processing.

I need to be ecnomical. Thanks.