Editing the General UI
Most of the Admin Page ui is in html files in the Server Side Code/views/ folder.
Since most pages have the same basic structure, most admin pages are generally placed inside template.htm.
Public pages are nested inside publictemplate.htm
Editing the Form Structure/text
The forms are being generated in Server Side Code/js/script.js.
Search and replace any form text you wish to change from this file.
Editing Notification Titles
When you add a new wallpaper the admin has the option to send a notification. The notification title can be changed from: Server Side Code/controllers/WallpaperController.php line 227:
$apiController->sendPushNotification($f3, $preferences->getValue("newitemnotificationtitle", "New Wallpaper"), $f3->get('POST.name'));
and for bulk line 305:
$apiController->sendPushNotification($f3, "News", $f3->get('POST.name'));
The general notification title can be changed from: Server Side Code/controllers/ApiController.php line 191:
function sendPushNotification($f3, $title, $body, $topic='news')