[Reference] Key to the Root and Upgrade Guides

I'll try to keep this updated, but please check post date of root/upgrade guides in the forum to make sure nothing later has come out.
If this list helps you, please post a "bump" (or thanks :) ) to keep it near the top of the forum for other people to see. Thanks!

• This applies to 2014 Fire HD 6 and 7 (4th gen HD)


• All guides include instructions for installing Gapps


• Credit: Guides for rooting any OS above 4.5.3 rely on Powerpoint45's instructions for downgrading to 4.5.3 to obtain root. Thanks @powerpoint45!

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Basic Root and Upgrade (for any Fire OS)

UPGRADE

Upgrade guides link back to root instructions, so you can just begin here.

• Upgrade to OS 4.5.4 or 4.5.5 (4.5.4 is minimal OS required for fully working Gapps)
  You can upgrade to 4.5.5 with either of these. The methods are different, so have a look at the intros.
  - [How to] Upgrade to 4.5.4 and keep TWRP and root: http://forum.xda-developers.com/fire...-root-t3141648
  - [How to] Upgrade to 4.5.5 (or other 4.5.x) with root in TWRP: http://forum.xda-developers.com/fire...-root-t3174449
  .
  


• Upgrade to OS 5.2 (Lollipop)
  - [How to] Upgrade to Lollipop and keep ROOT + GAPPS http://forum.xda-developers.com/fire...gapps-t3163950

ROOT

• Root, install TWRP, and upgrade
  - [ROOT, v2.0] + FireOS 4.5.4 + fully working latest GAPPS http://forum.xda-developers.com/fire...gapps-t3150613

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Detailed Root and Upgrade to Lollipop (only for never-rooted OS 4.5.4, 4.5.5, or 5.0.n)

• Step-by-step guide to root the listed OS's, install TWRP, and upgrade to Lollipop
  - [Root] OS 4.5.4, 4.5.5, 5.0.n and install Lollipop ("newbie friendly") http://forum.xda-developers.com/fire...1#post62188341

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Return to Stock

- [How to] Restore full stock FireOS http://forum.xda-developers.com/fire...ireos-t3164267

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Obsolete

- [ROOT] With working PlayStore Google Apps + Custom Launcher + superSU http://forum.xda-developers.com/fire...ustom-t3113311