Ipad Air

There no way to change that. You would need to restore in DFU Mode.

First: Put the device into DFU mode.

DFU MODE STEPS

1. Hold the Power Button (3 secs)
2. Continue holding the power button and also hold the home button (15 secs)
3. Release the power button while continuing to hold the home button (10 secs)
4. Your device should prompt with the "Connect to iTunes Screen"

Second: Plug it into your computer and open iTunes. It will either prompt to restore and up date or you can manually restore using the following steps.IOS Restore StepsBefore restoring:

• Verify that you are using the latest version of iTunes.
• Back up your device.
• Transfer and sync content to your computer.

Restoring your iOS device

1. Connect your device to your computer.
2. Select your iPhone, iPad, or iPod touch when it appears in iTunes. Select the Summary tab, and click the Restore button.
3. Click Restore
4. After a restore, the iOS device restarts. You should then see "Slide to set up". Follow the steps in the iOS Setup Assistant.
5. If needed, restore your device from a previous backup.

If you mean the passcode to unlock the iPad then you need to type in the current passcode and you can then change it via Settings > Passcode > Change Passcode

If you don't know the current passcode : Forgot passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support