In order to replace a set of piston rings in an engine you will need to remove the pistons themselves. This means pulling the head and dropping the crank.
The bottom end needs to come out. This means the crank has to be removed as well as the pistons. Then the rings can be replaced and everything reassembled.
the cylinder of the engine has to come off in order to replace the rings on the engine. you need in some cases to have a tool to reinstall the rings into the cylinder.