The Casio G-Shock line of watches has become a classic brand, featuring a wide array of designs dating back to production that began more than 10 years ago. Despite the variety in design, however, nearly all G-Shock watches can be adjusted in the same way. (The only exceptions are the watches that feature "atomic timekeeping" technology, which adjust their own time).
Press the "Adjust" button. It's usually the top-left button, slightly smaller than the rest. When you have successfully pressed the button, one of the numbers on the screen (generally the seconds) should begin to flash.
Choose which number you would like to change (hours, minutes, day, etc) by using the "Mode" button on the bottom-right to cycle through each option on the main screen. You'll know when you have reached your target position because that number will flash.
Use the top-right button (usually labelled "Start/Stop," or sometimes "Light on/off") to change the number once you have highlighted the position you wish to change. When you have finished making the desired adjustments, press the "Adjust" button again to complete the process.
Use "Adjust" on any screen of your Casio G-Shock watch. To reach the watch's other screens, press "Mode" (bottom-right button). Most G-Shock watches have four screens total, including the main screen. On each screen, use the same process described above to make adjustments to the time (with the exception of the stopwatch screen, which does not keep time.)
Note that on some adjustable screens, tools can be activated to change the function of your watch. To activate these tools, enter "Adjust" on any screen, then press the bottom-right button (usually labelled "Light"). Press "Adjust" again to return to the watch's display with the tool in place.
Available tools on most G-Shock watches are 24-hour mode (available from the main screen) and auto-timer (available from the timer screen).
Go slowly. When adjusting the G-Shock, numbers can only be increased. If you miss your desired number, you'll have to start over. If you have adjusted a screen and want to move to the next one to do the same, don't panic if you are first returned to the main screen. This is a standard feature of most G-Shocks. Use the "Mode" button again to return to the screen you would like to adjust.