How do you fix a flushometer?

A lady list moderator told me not to go into to much details on fixing things on here as she feels people are not able to comprehend advice (mentally to understand)

Without going into technical detail in order to give any advice one has to know if the flushometer is a piston or diaphragm type and and knowing if it is a Coyne Delany Rex, Sloan royal, Sloan Gem , Turn to silence flush boy would sure help a lot