Matthew,

There should be the same (nut and bolt) at the top end but you may have to tilt the backbox forward to get to it.  There is not always one there.

The rails are then stuck on with double sided tape.  I got my last lot (well the missus did) at spotlight (I refused to go in!)..

Use a heat gun or hair dryer to gently heat then with a scraper or similar under the rail gently pry it away....Take it slowly as can remove paint or decal...