What motherboard do you have?
And:
RAM (Random access memory) is not where your data (such as music, games, and other programs) are stored. That's your hard drive. When your computer wants to run a program it loads a copy into the ram and runs it from there (ram is much faster than a hard drive). Changing your ram will not cause you to loose your music or anything.
Depending on your motherboard you may or may not be able to put in the 512 stick. If it has a max of 512 it sounds like an older mobo... Look in your manual to see what you really have.