[header] How to replace the line on a black and decker trimmer [title] Turn off all power to your trimmer. [step] To safely replace the line on your power trimmer, it's important that it doesn't turn on while you work on it. Unplug the trimmer or remove the ion battery that came with it. 
This will ensure that you won't accidentally turn on the trimmer and injure yourself. [title] Sit the trimmer on a table or chair.