Right click on a song that opens with Windows media player and go to Properties
in the window that pops up there will be a button that says %26quot;Open With%26quot;, Click on that and change it from Windows media player to Realplayer.
Click apply and the icons for your music should change from a windows media player icon to a realplayer one. All your music will change automatically, If some of your music still opens with WMP it's because they are different file types. Do The same thing for one of those files and all the other files that are that type will change automatically.