twitch, if it is the older girls which have stopped laying - commercials such as ISA brown over 2 years, and others over 3 years you could despatch them as no longer being economical to keep. Any thing younger, as Kirane said, is probably just taking a well earned break.
My preferred method is a very sharp tomahawk. Hold them by the legs with their head on a log (legs up higher than head). Wait till they stop flapping, then one quick, accurate chop to the back of their neck - off with their head and straight into an old feed bag. Be aware that they will continue to flap and struggle, even after they are dead - this is a muscle response, they are brain dead and not aware of what their body is doing.
Don't try this if you are not confident with your aim - you need to be quick and accurate and need to keep your own body parts intact.
There are other methods, including a special killing cone which you can buy. These are apparently very good - quick and easy to use, with no blood.