Uninstall phpBB 3 Style
phpBB 3 styles have 3 components: template, imageset and theme.
1. Removing Style
First you have to remove style. To do that go to admin control panel, click “Styles” tab, and delete style. This will remove style.
2. Remove Components
After removing style, you can’t remove files yet, because there are still style components installed. In admin control panel in styles tab click “Templates”, and uninstall template used by that style, then do the same for imageset and theme.
Do not uninstall template, theme and imageset if you still have some style installed that uses them. First you must uninstall all styles that use them.
After uninstalling everything, you can safely remove files.