there are 2 sorts some that have a top hat fitting over the hose to clamp it down and the newer sort which dont
*first you need to slide up the top hats, best done by pushing then up from underneath with a screwdriver or a pair of plyers...dont get hold of the main part of the top hat with plyers as you will crush it.
if you dont have top hats on skip that bit
*pull the hose off the barb....this may be hard, especially if you have the type of barbs that use top hats.
replace the hose with new hose, make sure its long enough and not kinked or pulled tight, i always leave em a little long deliberatly. dont forget to put the top hats on the hose before you push the 2nd end on
*replace the top hats
done