Thank you for advices! I installed Android 5.1.1, but to make it work, manual formatting Data and Cache in ext4 was necessary. Installation of Nethunter was smooth.

Hello, I recently bought a Nexus 5 Hammerhead from the second hand with installed Ubuntu Touch. Now I'd like to test Nethunter but I have no idea how to switch OS - all the tutorials and threads are about going from Android to NH, but what should I do if I want to move from UT? Is it necessary to install Android first?