Version 0.9.3919 is effectively just the smallest possible update for iOS 9.

To enable, disable, or change the order of themes, see the WinterBoard panel in the Settings app: there is no standalone app as of version 0.9.3916.

Wallpaper (whether png, html, or any of the other crazy formats that I should never have added to WinterBoard) is not currently supported on iOS after 7 :(.