Far as I know, only way is to open the skin folder in Explorer & delete any
*.wb4,
~*.* &
*.*~ files (there should only be 4-7 total, easiest way to find is to sort onType), then re-apply the skin. Those files amount to the skin's 'cache'.
Many have been requesting, for a long time now, that a 'button' or menuitem to accomplish this be placed in WB Config (better yet, the tray icon's context menu) but the request has fallen on (apparently) deaf ears so far.