Hey guys, struggled with this too, but found the answer on another forum.
# Press and hold the '''TIME''' button or '''CLOCK''' button for more than 2 seconds, until two numbers flash on the screen.
# Change this number using the + and - buttons on the back to the correct year (20xx, where xx correspond to the year). Press the '''TIME''' button or '''CLOCK''' button.
# Enter the correct month and date (in this order for the EU version at least) using the + and - buttons, and press the '''TIME''' button or '''CLOCK''' button.
# Press the '''+''' button or the '''-''' button to select the time as required, then press the '''TIME''' button or the '''CLOCK''' button.
You can always start at 1 again if you incorrectly fill in the time/date/year.