Check the manual! I think in netspeak it's "RTFM"!
Every furler is different. Just in case you have a Selden Furlex like mine are, the basic principles are like this:
1. There is a chrome plated sheet metal guard which is attached to the furling
line fairlead with four screws. Take out those screws plus the two clamping the end of the fairlead to the back of the guard, and you can remove the guard, and the fairlead will disengage from the locking block below the furling
2. Now you can get at the furling drum itself, which as you will see is in two parts
held together with Torx screws. Take these out and separate the two halves.
3. The end of the furling line goes through the hold in the middle of one half of the furling drum and bends over to be clamped under the inspection
hole. It will be obvious when you have it apart how it works. Once the line is in place, clamp the furling drum back together again. The inspection
hole exists so you can see that the end of the line clamped down in the right place.
4. Take a couple turns around the drum (the sail is all the way out, right?) before putting everything back together again. Be sure the furling line fairlead is aligned in the right direction before you tighten the bolts.
That's it. Easy peasy. If you don't have a Furlex, you will need to rummage in your collection of manuals
or get the appropriate manual online. The Furlex manual is available here: http://www.seldenmast.com/page.cfm?id=6597