I'm using the black ups darkness theme but it has this plain black wallpaper. How do I change that to a wallpaper of my choice? I'm having the hardest time figuring this out.. thanks in advance.
you can ssh into your phone and go to var/stash/themes find the theme and replace the wallpaper.png(or whatever the file extension is) with the one you want, but be sure to rename it exactly as it is listed in the theme folder.
or instead you can just rename the file adding a 1 at the end ie. Wallpaper1.png and then you will be able to change wallpapers like usually through the settings menu.
You could also use iFile to rename the file from the phone without SSHing in. You will find it under var/stash/Themesxxxxx and the name of your theme