I recently updated Realplayer and it has now changed all my media/music files to its default setting so I can only open them into Real player at the start. How can I change them back to Wmp files?
It hasn't changed your files at all, it just changed the program that is associated with them.
right click on any of the files, select open with > choose default program, make sure always use this program to open selected files is is ticked and then select the program you want them to open with.