Apple's official instructions to restore an iPad are:
1. Connect iPad to your computer.
2. Select iPad in the iTunes sidebar, then click the Summary tab.
3. Click “Check for Update.” iTunes tells you if there’s a newer version of the iPad software available.
4. Click Restore. Follow the onscreen instructions to complete the restore process. When restoring, it is recommended that you back up iPad when prompted. When the iPad software has been restored, you can choose to set up iPad as a new iPad, or restore your music, videos, app data, and other content from a backup.
Please additionally note that Apple staff also cannot unlock an iPad for you without restoring the iPad, which will erase everything on it.