The time should automatically change. What is likely, is that you do not have your time zone set properly.
For the Sharp SPC374T Atomic Clock - Time Zone setting- Press the 'Time' button once, the time zone will show where 'Day' usually is, use the Up or Down button to adjust.
All settings adjustments of the clock:
Remote Temperature: Important note install the batteries in the remote sensor first, before you install batteries in the clock. if the sensor will not detect you need to manually search for the sensor. Make sure the channel settings are correct on the remote sensor and the clock (Default Ch1) Press and hold the Test Button, the channel display will blink. If you still cant get it to work try it in the same room. If it still wont work. Press The reset button on the clock and sensor then try again. If it still wont work buy a new clock.
Set the Time Zone: press Time button once to view current zone, press up or down to change the zone, press the Time Button to exit the setting mode.
Set Time and Date: press the Time or Month/Day button for 3 seconds to set. use up and down to change value
Radio Control Time:Once the batteries are installed in the clock the clock will begin to seek out the signal to update the time this will take 5–8 minutes if 8 minutes has gone by recommend setting time manually. Otherwise you can press the Receive button to tell the clock to seek the NIST WWVB signal. The clock will only search for signal at night automatically @17:00 and 02:00. If the radio icon is flashing in the clock area the signal is received ok, if none or part of the icon is showing the signal is poor or not working correctly (the icon is a satalight looking thing with 5 ‘radials’ that blip towards the main icon), relocate your clock or try later. It is recommend to set the clock manually then let the automatic control take over.
The 12/24 button will set ‘military time’ the Min/Max button will show the current min or max temp on record for the sensors. The Alert button is for setting a alarm to the temperature sensors, note that the time alarm must also be on for the temperature alarm to activate.