Can you provide us with the applications/programs that you are using when it is freezing up? Check the system requirements of these programs that you are trying to use and if it is meeting the specification of your computer it might be something else. Most of the upgrade-able peripherals for laptops are HDD, RAM and processor.
Hello, and thank you for your post. As Killer above suggested, check your running programs to determine what is causing your poor performance before turning to Hardware for a solution. VAIO Care or at the very least reviewing the "Performance Information and Tools" category in your Control Panel may help resolve your issue.
However, to answer your question, the only user upgradable item in your laptop is the memory.