TimeAlarms Library: how to update the timer?

[Tomasina]

For example:

byte powerOn_Hour = 7; 
byte powerOn_Minute = 30;
byte sensorUpdateInterval = 120;

void setup() 
{
  Alarm.alarmRepeat(powerOn_Hour, powerOn_Minute, 0, LEDsOn);
  Alarm.timerRepeat(sensorUpdateInterval, readDHT22);
}

void userSetValue() 
{
  powerOn_Hour = 9;           // <-- Value updated. How to update timers?
  powerOn_Minute = 0;         // <-- Value updated. How to update timers?
  sensorUpdateInterval = 30;  // <-- Value updated. How to update timers?
}