How do I restring a Ryobi Model #30550 weed eater - dual string

Rethreading a weed eater is not too difficult. All you have to do is buy a new spool of the plastic line, and then carefully remove the old one. Then you pull out a bit of the new spool so it sticks out past the opening (about two inches will do) and snap the new spool in.

Hi,
I realize a different name is on this manual, but the machine is made by Ryobi and it has an excellent section on reloading heads.
Bolens 2-Cycle Gas Trimmer Operator's Manual | ManualsOnline (http://lawnandgarden.manualsonline.com/manuals/mfg/bolens/bl150.html)
Peace,
Clarke