Screen size of W580i is 240X320.
You can Delete skins by FAR manager of XS++ 3.1 easily.
For XS++ 3.1:
Simply go to the SFX. and then Click on Start SFX.
Then go to \tpa\system\multimedia\mp\skin
You can find your Walkman 2 skins
Then select a skin folder and Press Delete.
Lastly Press Shutdown.
For FAR manager:
Connect the phone with FAR manager.
Simply go to \tpa\system\multimedia\mp\skin
Select any Walkman 2 skin and delete it.
Lastly shutdown.
So simple :D
Good Luck.