If you need to change the head on your Dewalt string trimmer, you can do so fairly easily. The first thing you'll need to do is remove the old head. To do this, unscrew the knob at the top of the head counterclockwise. Once the knob is removed, you should be able to pull the head off of the trimmer. Next, take your new head and screw it onto the trimmer in the reverse order – screw on the knob clockwise until it's tight. And that's it! You've now successfully changed the head on your Dewalt string trimmer.