There are four steps in order to unlock/restore your ipad when your passcode had been forgotten. The steps are as follows:-
1) Connect iPad to your computer.
2) Select iPad in the iTunes (need to download and install) sidebar and click the Summary tab.
3) Tap Check for Update. At this moment, iTunes will tell you if there’s a newer version of the iPad Mini software available.
4) Tap Restore and follow the onscreen instructions to complete the restore process. When the iPad software has been restored, you can choose to set up iPad as a new iPad.