To replace the chainring on a Shimano Hollowtech crankset, you first have to dismantle the cranks in order to remove the right hand crank. The chainrings are connected to the crank via chianring bolts that require a special tool to tighten and loosen. You may want to replace a chainring because the teeth are worn, or because you want to adjust the gearing ratio.
This is a long guide, so you can choose to either watch the entire video above, or follow it in smaller chunks by clicking on the individual steps below.
Steps to Replace The Chainring On A Shimano Hollowtech Crankset:
Modern bikes usually have cranks made of aluminium, they are mounted on an axle made of harder material, usually steel. If there's any play between the cranks and the crank axle the soft aluminium will soon get worn to the point where it's impossible to lock the cranks. If the cranks are loose don't ride the bike.