Turn off the trimmer motor and lay the unit on the ground with the head facing up.
Hold the trimmer drum and twist the spool on the end of the trimmer clockwise to remove. Remove the spool from the drum.
Remove any string remaining on the spool and discard.
Insert a piece of trimmer line, approximately 20 feet long, into the loop inside of the spool. Pull the trimmer line through the loop so that one end is approximately six inches longer than the other.
Place your index finger on the trimmer line to hold it tight, then wind the string around the spool in the direction of the arrow. Make sure that the string is wound tightly and evenly.
Wind the spool until approximately six to eight inches remains, then feed each line through the eyelets on the housing of the spool.
Turn the spool upside down and feed the line through the eyelets on the drum. Align the spool with the drum and push the spool into the drum.
Pull both lines to free them from the notches, and turn the spool counterclockwise to lock it into the drum. Trim both lines to the desired length using scissors.