Set the trimmer on a flat workbench, with the cutting head facing up. Twist off the cap on top of the cutting head counterclockwise. Remove the cap and slide off the spool.
Discard the old spool; clean the cutting head and cap thoroughly with the rag. Install the new line into the new spool; hook one end of the line into the slot found under the spool, allowing no more then 1/8 inch to protrude. Wind the line in the direction of the arrow found on the spool. Wind in level rows, between the flanges in the spool; do not exceed 30 feet of line.
Insert the spool back into the cutting head, and the line through the eyelet. Hold the line and the spool in place, place the cap over the spool and turn the cap clockwise until tight.