How to change the serial number for your Trend Micro Internet Security product.
You need to open the Trend Micro Internet Security Main Console. This can be done from the little red icon in the 'system tray', down the bottom right near the clock. Click the icon and then click 'Open the Main Console'
Now click the expiry date at the bottom
Click Change your serial number
Type the new serial number in the fields provided, click next then close