New answers tagged downgrade
Once you get to the USB logo, press the volume up and down together once and it should bring you into recovery.
You can find the easiest tutorial to downgrade your device here : Downgrade Lollipop to KitKat You have to wipe/ factory reset the device and flash the Factory Images to downgrade the Android version.
This is how you can do it: http://thetechrism.com/downgrade-lollipop-kitkat-nexus/ You can't do it without doing some sort factory image/reset. Google has not officially distributed version of KitKat, however. So you'd have to use third party.
It is unlikely, since the Nexus 9 was a Android 5.0 Lollipop launch device. There are no official (Google developed & distributed) versions of Android 4.4 KitKat for the Nexus 9. Third party roms would be the way to go - but I have found no KitKat roms for the Nexus 9, and I personally doubt one would be developed unless there was a massive interest in ...
Is there something I can do that is safe to return to the old OS? Easy answer: No, there is not. You should flash it manually using, for example, flashtool (you don't need root). Here is great guide which may help you. Chance, that you hard brick your phone is really small If you flash right firmware.
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