How do you change the trim line on a ryobi 700 gas trimmer. I do not have the manual.

Just above the trimmer head right where the aluminum shaft meets the head there should be a hole the size of a nail. Stick a nail in the hole and slowly rotate the head, it should drop into a slot and lock the head from turning. Take hold of the knob that bumps the ground and unscrew it. As you remove the spool carefully observe how the line feeds through the spool and head and replace the same way or just buy a pre filled replacement spool.