Capacitors in a voltage regulation circuit
If you look at the data sheet you will see that the minimum requirement is a 330 nF capacitor on the input if the regulator is situated some way from the rectifier reservoir capacitor and a 100 nF capacitor on the output to improve stability and transient response. Those are the minimum requirements for the regulator itself. Additional capacitance is often provided for the circuit that is being powered; it depends on the characteristics of the load, and 100 uF is a popular value for most applications. I wouldn't worry much about the value, and use whatever you have.