This topic has been covered several times. The upgrade was initially available but lately stopped due to problems with phones that Bitlocker enabled. Yes, they plan on resuming the upgrade to DP users in the future but nobody knows when or if they will be unable to do so for technical reasons. In the meantime, you have to flash with the Nokia Recovery Tool, wiping out everything on the phone. Depending on your phone or carrier, you might directly get Cyan and 8.1 after flashing or you might get Black and 8.0 and have to perform a Phone Update to get Cyan and 8.1.