To delete all of your music files from the Player, you will have to multi select all the files. Here is a simple way to do:
1. Open RealPlayer.
2. Go to your Music library.
3. From the dropdown, choose All Music.
4. Select the fist file and then press Ctrl + A on your keyboard. (This will select all of your music files)
5. Click Delete on your keyboard.
Please note: You will be prompted if you want to delete them from RealPlayer library. There is a Check box also where you will be asked if you want to permanently delete it from your hard disk as well. If this is checked, your music files are deleted permanently and can't be retrieved. Therefore, please read the messages carefully before you delete them.
Please follow the instructions from this link to change the email address on your account.