[Q] How can I change my ROM correctly? topic

Hello everyone! Happy Christmas!!!! :D

Firstly I want to tell I don't know if I'm in the right forum to explain my doubt. SORRY!! I'm new here and I don't know anything yet. Well, anyway I'll tell you my doubt and I'd be grateful if you could help me. My phone is Samsung galaxy trend plus gt-s7580 free (bought in Spain), and it has the version PHE. I'd like to install United Kingdom's official version (BTU) by Odin. What should I do? I know how I have to do by Odin and then I have to do reset to the wipes. is this enough? I´d like to have my phone how if I would have bought in UK, I don't want to install BTU over PHE. Can anyone help me please??? Thanks.

[Q] My new nexus won't start correctly topic

Hello, I'm pretty much new to the android scene therefore excuse me for my stupidness on this field :(
I unlocked my nexus 6, then I rooted it and and then I flashed a custom rom (Euphoria 1.0) with WugFresh's Tool.
Yesterday I tried installing adaway and gave it full root permissions, it asked me to reboot and I did so.
After rebooting I realized that I can't unlock my phone nor do anything else except using the pull down notification bar and having a back button, no middle button nor right button.. The screen just remains black. I tried rebooting in recovery mode but nothing changes.
What do I've to do now?
The device doesn't show up as MTP.
When I enter TWRP now it asks me for a password??
I've a Nandroid backup saved on my HDD and I still have the custom rom ZIP saved as well.