The picture on the main (home) screen and the theme are two different things and can be separated. Like someone said before me. Delete the new theme and change to the default or keep the new theme and select the default. It depends on if you want to keep the new theme for use later........... Good Luck
To change your theme click on your Options icon then click Theme. You will see a list of themes installed on the phone and a preview of it when you scroll over the name. Click the trackball to select your desired theme.