Turn pedometer on (shake the unit) and push the MODE button until you see "STEP" in the upper right corner.
Hold down the MODE button for 3 seconds and "12/24 Hr" will flash.
To change the clock format from "12 hours" to "24 hours", push the SET button once; if not, skip this step.
Push the MODE button a second time and the hours will flash. Use SET button to set the desired hour.
Push the MODE button again and the minutes will flash. Use the SET button to set the desired minutes.
Once you have set the time, push the MODE button 5 more times until the display stops flashing to save and exit.