You'll need to make iTunes your default player. Go to your LW library, click on Saved Files then click Explore. Now your saved folder will open.

Right click a music file > open with > choose program. Choose iTunes from the list & tick the box to always use the selected program to open files of this type > ok

If you still have probs with WMP opening files, open WMP > tools > options > file types. Untick the boxes beside the file types that you don't want WMP to play > apply > ok.

That should do it.