If you want to REPLACE a music player:
Press on the player and click on the "Replace" icon on the bottom menu
If you want to upload your music:
Click on the "Media" icon in the left menu >
"Music" and upload the music you want from your comp. or from a URL!
Press on the player and click on the "Playlist" icon on the bottom menu,
add your songs!
If you want to upload your own stuff:
Click on the "Media" icon on the left menu >
"My Media" >
Choose the type of media you want to upload.
Follow the prompts to upload from your own comp. or URL