No, I have meant the background picture (lt_school: auditorium picture) below the slider where only a gap is shown when you move up and down.
Do you mean it’s slider below the menu bar? If so, you can change it via Administrator >>> Component >>> Unite Revolution Slider >>> Slider >>> Edit Slider.
I have meant the background picture (lt-school: auditorium picture) where a slit is shown when you move up and down on the page.
Is it a picture you’re mentioning? http://take.ms/GUxoI
If so, it places in ‘images/ltheme_sampledata/parallax.jpeg’, you can see delete and replace with another image easily via FTP or go to Administrator >>> Content >>> Media Manager.