Unplug the extension cord from the Toro electric trimmer. Place the trimmer on its side so that you have access to the trimmer spool.
Hold the trimmer spool by its side with one hand. Twist the cap on top of the spool counterclockwise with your free hand. Remove the cap from the spool.
Lift the spool out of the Toro trimmer. Remove any remaining string from the spool. Take the spool to a home improvement center or Toro dealer for a replacement prewound spool.
Insert the new spool into the Toro trimmer head spool housing with the end of the trimmer line inserted through the eyelet in the housing. Hold the trimmer spool and twist the cap over the spool in a clockwise direction.