sorry about that, i think I'm typing to fast...
my previous post should have read:
the upgrade will only effect any customizations you have made to the files of power store outside of the themes folder, it will _not_ effect products in the database, product images or content added through the content management system.
for each theme, a new folder is created in the webassist/themes folder. to delete a theme, _delete_ the folder for that theme.