DHL wanted a smaller aircraft for routes that could not support larger planes like the 757 or 767, so they decided to convert a BN737 into a cargo plane for item delivery. The whole process started in 13th of November 2013 and ended on the 9th April 2014. Take a look how it looks like.
Full album is here: Boeing 737 conversion to a freighter
http://i.imgur.com/qlvLltZ.jpg
http://i.imgur.com/mgxN5Yk.jpg