HP Laptop: How to reduce physical memory  

I bought the HP Laptop (entertainmnt series) in Feburary 2008. It has Windows Vista.Since then a lot of activity has happened on this poor thing. Loading and unloading various programmes and features, games and visiting arbit sites in the hope of getting online work and freebies. I know, sounds like how can someone be such a dud. But when you have a lot of time at your disposal then you tend to do such things. I don't know about others but I did. And now my poor friend, the laptop, is facing serious issues with its physical memory. No marks for guessing that it was done through all the overload of installing and un-installing. I guess? I am not very technically sound but have an idea that if I reformat my dear laptop then it will get a new lease of life. But if I do so then all the important documents might be lost. I know, you guys will suggest to move the information to some other source, either online or physically. But, lazy me, cannot handle so much of extra work. Many will say, Vista is sad. It is any day slower than XP. But that doesn't solve my problem. So how can I reduce the physical memory of my laptop? Any good souls who are willing to help with a genuine solution please leave a note for me. I would be glad to give it a try and see if it works. Hopefully my dear laptop, who seems slow, lethargic and gives up running a programme at times, will spring back to its old self.