Need to Move, Realign, or Expand My Background

Unfortunately you cannot realign your background image.  The anchor and origin point of your background is in the upper left corner of your image. This means if you want to expand your existing map, you can build out down and to the right. As long as your newly uploaded background covers the current image's areas, the impassible tiles placed should continue to exist rather than being erased, which happens when your background image does not cover the same area.