There is no way to reset it.
You have to restore the device within iTunes. You want to use the same computer that you always sync with so that you can restore your app data and settings. You can restore with any other computer, but you will lose everything on the iPad.
Instructions can be found here.
You will probably need to restore using Recovery Mode. You can read about it here.
Or you can follow this.
Recovery Mode Instructions
- Disconnect the USB cable from the iPad, but leave the other end of the cable connected to your computer's USB port.
- Turn off iPad: Press and hold the Sleep/Wake button for a few seconds until the red slider appears, then slide the slider. Wait for iPad to turn off.
- If you cannot turn off iPad using the slider, press and hold the Sleep/Wake and Home buttons at the same time. When the iPad turns off, release the Sleep/Wake and Home buttons.
- While pressing and holding the Home button, reconnect the USB cable to iPad. When you reconnect the USB cable, iPad should power on.
- Continue holding the Home button until you see the "Connect to iTunes" screen. When this screen appears you can release the Home button.
- If necessary, open iTunes. You should see the recovery mode alert that iTunes has detected an iPad in recovery mode.
- Use iTunes to restore iPad.
If you mean the passcode to unlock the iPad then you will need to connect the iPad to the computer that you normally sync to and you should then be able to reset the iPad and restore/re-sync your content to it (http://support.apple.com/kb/HT1212) - you may need to put the iPad into recovery mode in order to be able to reset it : http://support.apple.com/kb/ht1808
If you do it via a different computer then :
If you restore on a different computer that was never synced with the device, you will be able to unlock the device for use and remove the passcode, but your data will not be present.