Generaly you just get a lighter
line and attached it at the tail. I use duct tape to join them but sewing it is more secure. Then you pull the business end out from the mast head and the messenger
line will follow.
Once you have the old haliyard out detach the messenger
line and reattach to the tail of the new
line. Then pull the messenger
line out at the exit in the mast and the new halyard will go up and into the mast head. Once it is through at the exit point you are all done.
PS nice boat.