The chainrings on your bicycle are the large gear cogs that connect to your pedal crank arms and drive the chain. With regular riding, the teeth on these chainrings become worn due to friction. A worn chainring can cause the chain to become sucked between the teeth and bunch up. When this happens, your bicycle will slip out of gear, have difficulty shifting or the chain can fall off entirely. To prevent this, you will need to replace the chainrings when they become worn.
Lift the rear wheel of the bike off the ground enough that it can turn, and then pedal forward and shift the chain onto the smallest sprocket in the rear. Pull on the lowest section toward the chainrings so you create enough slack that you can take it off the chainrings and rear sprockets.
Insert an 8 mm Allen wrench into the center bolt of the right crank arm. Turn the Allen wrench counterclockwise while you use the crank arm for leverage. Once you fully unscrew the bolt, take the crank arm and chainrings off the bike.
Locate the five bolts that screw the smallest chainring to the crank arm. Insert a 5 mm Allen wrench into one of the bolts and turn it counterclockwise until you can remove the bolt. Take out the remainder of the bolts. Draw a mark on the replacement smallest chainring to mark its position in relation to the crank arm, and then take off the old chainring.
Insert the chainring nut wrench into one of the nuts holding the two largest chainrings together. Turn the chainrings over and place the 5 mm Allen wrench into the bolt corresponding to the nut the chainring wrench is holding. Turn the Allen wrench counterclockwise until the bolt and nut are removed. Remove all the other bolts and mark the position of the new chainrings in relation to the crank arm.
Assemble the new chainrings onto the crank arm, beginning with the two largest. Line up the marks on the chainrings with the crank arm. Apply a dab of grease to each of the chainring bolts. Place one of the chainring nuts into the middle chainring and the bolt into the hole on the other side of the crank. Tighten the bolt in place and then secure the remaining bolts.
Put the smallest chainring into place on the crank arm and secure it with the final bolts to a hand-tightened level. Tighten each of the bolts a quarter-turn while moving in a star pattern around the chainring. Stop once the final chainring is secure without the bolts being overtightened.