Replacing string on a Ryobi weed eater is not as simple as just wrapping one string around a spool. The Ryobi weed eater uses two strings which you will need to replace at the same time. There are pre-wound replacement spools available at home improvement centers. The most cost effective choice is to purchase bulk trimmer string and install the string on the existing Ryobi weed eater spool.
Place the Ryobi weed eater on its side on a flat surface with the gas filler cap pointing toward you. This will prevent accidental fuel spillage. Grab the end of the spark plug wire where it connects to the spark plug. Twist the spark plug wire slightly and pull the wire off the spark plug.
Grab the side of the trimmer head with one hand and turn the spool retainer counter-clockwise. The spool retainer, or bump feed, is on the center of the trimmer head. Remove the spool retainer from the trimmer head.
Pull the string spool out of the trimmer head housing. There is a spring that attaches to the bottom of the string spool. The spring should stay on the string spool.
Cut two 9-foot pieces of monofilament string from your bulk string line with a pair of scissors. Lay the string spool on a flat surface with the spring pointing toward you.
Insert one end of a piece of string into the hole in the upper part of the string spool. The hole will be in the middle of the upper string channel. Wind the string around the upper channel counter-clockwise until you have 6 inches of string remaining. Place the end of the string into the nearest string slot in the upper part of the string spool.
Insert the end of the second string into the hole in the lower part of the string spool. Wind the string counter-clockwise and place the remaining 6 inches into the lower string slot.
Place the string spool inside the trimmer head housing and guide the ends of the string through the two holes in the housing. Place the spool retainer over the string spool and turn the retainer clockwise to tighten