From the Windows Phone Preview for Developers page s n n You cannot revert or return to a prior operating system release version after you have updated your phone to a preview update. We will move you forward to a released state but we cannot take you back to a prior released state.n For most people on the Developer Preview programme the best advice is to simply wait until the official 8.1 update bes available from their phone manufacturer and carrier (e.g. in Nokia's case the Lumia Cyan update)