Unmoveable background ?

HI im using Mason prebuilt theme. It has the building at the start of the site (first image), how do i get rid of it. i have added a background url and yet the images is under it and shows on the side, ive gone throuight the elements and changed them to a colour and activated background and changed the blank url here to a colour as well and the building still shows up. ive tried a lot of other things as well, basically how do i get rid of this ‘legacy’ image