Mary Lou,
The downhaul has taken many different shapes over the years, but it  
basically stretches the sail by pulling it down, much easier than climbing the  mast 
and trying to stretch it to the top. :)
The sail simply slides out of the furling tube once you have removed the  
attaching screws. Depending on your bearing type, the bearing may have to  be 
removed on the end you plan to slide the sail out of. Keep screws and  bearings 
separate and well marked. I like to take digital pictures when I do  this to 
remember how things go back together. Unless you are taking it to a sail  loft, 
removing it from the tube is not necessary. However, should you remove it,  
getting it back in the slot can take time, but it is possible with a little  
effort. All of this should be done on a flat, smooth, dry, clean surface.  Unless 
you want to really extend the amount of time required to do this job, do  not 
remove the forestay from the furling tube. 
 
Rummy
 
PS. Be sure to properly support the furling tube so it doesn't bend. Any  
bend in the tube will make furling a lot harder.