Software and Hardware Upgrades

I have recently performed a check on a computer, i found that this computer was still using an old OS (operating System), this is a computer that is need of an upgrade to a new and better OS, i believe that upgrading to XP is a good choice for the computer it shall amke the computer a lot more usable, the computer needs its memory upgrading so that the OS can be installed, this is my first step to be completed...