Hello everyone,
I read a lot of threads regarding my problem but couldn't find the solution. Could someone kindly help me?

I have a TVbox with S905x and Android installed, I would like to install armbian, I downloaded the ISO, renamed the u-boot file for S905x to u-boot.ext and modified the file "/extlinux/extlinux.conf" leaving only the line without comment with S905x.

When I do "update" from Android it makes me choose a .zip file, copy something and then reboot.
Unfortunately, however, the system restarts with Android as if nothing had happened.

What am I wrong?
Thank you very much.

Have you followed the instructions in this FAQ post: 

 

Also, I would recommend using the toothpick method.  You need to have a specific type of 'update' andoid app installed for that method to work and I have found that a lot of android boxes don't have the right update app to use that method.  I always use the toothpick method to install multiboot.