How do I change a flush?

Depends what type low level high level close coupled which? Throw away flush? not heard of them before
are you in UK.
Obviously in all cases turn off the water.

Close coupled: Flush or bail out the water.
Undo the water feed pipe release from cistern.
Undo cistern wall fixing points.
Unod the wing nuts on bolts holding cistern to pan.
Lift cistern clear. the doughnut shaped seal between pan and cistern has to be replaced.
Turn the cistern on its side and release the syphon nut ease out the syphon. if it has ball float you may have to remove it held by plastic clip/pin at water inlet. Reverse on reassembly
Low & High level: Have flush tube from cistern to back of pan.
Flush bail out water. Undo flush tube nut remove flush tube. Undo syphone nut ease out syphone.
Reverse to replace.

Nobby
January 2009