There should be a hose clamp holding it in place. A hose clamp is a metal cuff which encircles the drain hose where it joins the washer and secures it into place. On the side of the hose clamp is a set screw which can be turned counter-clockwise with a regular screwdriver to loosen it. (Remember: Righty - Tighty, Lefty - Loosey) The hose should then slide right off. Be sure to have a bucket and old towels handy since there will be residual water left in the hose and in the body of the washer itself. The hose clamp may be rusted, in which case I recommend using PB Blaster (you can use WD-40, but I prefer PB) to loosen the rust and aid in the loosening of the set screw.
To remove a drain hose from the machine, make sure the machine is unplugged. The hose should be lifted from the drain pipe to a bucket for any residue to be emptied. The, unscrew the clamp that holds it at the back of the washer and remove it. You can read more details at www.ehow.com/how_5135778_replace-washing-machine-drain-hose.html.