Turn off the trimmer and disconnect the spark plug wire or remove the battery
Remove the trimmer head cover by pressing the tabs or unscrewing it
Take out any remaining old line and clean the spool
Cut a length of replacement trimmer line to the correct diameter for your Stihl model
Fold the line in half if using a dual-line spool
Insert the line into the spool slots or center hole
Wind the line tightly and evenly in the direction shown on the spool
Leave equal lengths of line on both sides if required
Thread the line ends through the eyelets in the trimmer head
Reinstall the spool into the housing
Snap or screw the cover back on securely
Pull the line ends to release the line from the retaining slots
Reconnect the spark plug wire or reinstall the battery
Test the trimmer at low speed first