How do I make my PC faster???

this crap is plug and play right??? I am a noob when it comes to the insides of a pc. right now I only have 256, if I buy a gig can I just pull my old RAM and install the new crap and keep everything thats on my pc now?? all my programs and shit? all my programs and files store on my HD right??? Bare with me everyone

or what about just buying 512 and adding it to my already 256?

main goal is to stop the PC from running real slow after its been on a for a few hours. I am happy with its performance and Plan to buy a new pc next year. Just need this one til then. if I can spend say 5-60 or so on RAM and it fixes the freezing problem that I am having then I am all for it.