You cannot with that unit. It is available as CE or Android. But keep in mind ONE very important point. The WinCE being provided is almost 2+ years old and will be losing support soon. Windows Mobile 7 (WinCE 7) is just about to be released and no plans (as always) for MS to support the older version or extended development
BTW: As far as I know, WITS A81-E can do one OR the other. There has still not been a dualboot firmware released.