[Fire HD 6 and 7 General] DoLooper:
These guides are for 2014 Fire HD 6 and 7. Don't use for any 2015 model. If your device has a micro-SD slot, it's 2015.

All root/upgrade guides install Gapps

Credit: Guides for rooting OS above 4.5.3 rely on powerpoint45's instructions for downgrading to 4.5.3 to obtain root. Thanks [MENTION=4469251]powerpoint45[/MENTION]!

Basic Root and Upgrade

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

Upgrade to Lollipop

- [TUT] Install [FireOS 5.1.2, Feb 26, 2016, "blue shade"], ROOT & GAPPS http://xdaforums.com/fire-hd/general/how-to-upgrade-to-lollipop-root-gapps-t3163950

Upgrade to OS 4.5.5

- [How to] Upgrade to 4.5.5 (or other 4.5.x) with root in TWRP: http://xdaforums.com/fire-hd/general/upgrade-to-4-5-5-root-t3174449

- [How to] Upgrade to 4.5.4 and keep TWRP and root: http://xdaforums.com/fire-hd/general/how-to-upgrade-to-4-5-4-twrp-root-t3141648

ROOT​

Root, install TWRP, and upgrade

-[ROOT, v2.0] + FireOS 4.5.4 + fully working latest GAPPS http://xdaforums.com/fire-hd/general/root-v2-0-fireos-4-5-4-gapps-t3150613

Video Root and Upgrade to Lollipop

Step-by-step video guide to root and upgrade to Lollipop

- OS 5.0 + ROOT + GAPPS + Play Store VIDEO TUTORIALhttp://xdaforums.com/fire-hd/general/os-5-0-root-gapps-play-store-video-t3238734

Return to Stock

[How to] Restore full stock FireOS; http://xdaforums.com/fire-hd/general/how-to-restore-stock-fireos-t3164267

Obsolete

Detailed Root and Upgrade to Lollipop (for never-rooted devices)

Step-by-step "newbie friendly" guide to root and upgrade to Lollipop

- [Root] OS 4, 5.0.n and Install Lollipop & Gapps ("Newbie Friendly") http://xdaforums.com/fire-hd/genera...lipop-os-5-t3172408/post62188341#post62188341

Out of date as of 3/3/16

- [ROOT] With working PlayStore Google Apps + Custom Launcher + superSU http://xdaforums.com/fire-hd/general/root-supersu-stable-appstore-custom-t3113311

Install ADB Drivers for Windows

Illustrated - Run ADB in normal and sideload mode from any folder location

- [GUIDE] Install Windows ADB Drivers for Fire HDs ("Newbie Friendly"): http://xdaforums.com/fire-hd/general/guide-install-windows-adb-drivers-fire-t3189000

Video

- Install ADB USB Drivers for Fire HD 6/7 (normal & sideload mode) (Windows): https://www.youtube.com/watch?v=CyJlmTtLsIg

Other Good Stuff

Temporarily Install TWRP on Rooted OS 5: http://xdaforums.com/showpost.php?p=62011272&postcount=2

Links to Stock ROM Update bins

Fire HD ROM links : http://xdaforums.com/fire-hd/general/fire-hd-rom-links-t3173102

Lollipop Info, Issues, Tips/Tricks and Workarounds

[Discussion] Lollipop on Fire HD : http://xdaforums.com/fire-hd/general/qa-lollipop-fire-hd-t3167532

Disable OTA, Amazon Launcher, Appstore and More

[How To] Disable System Apps and Services (includes OTA): http://xdaforums.com/fire-hd/general/how-to-disable-apps-services-includes-t3165348

Use a Script to Disable/Enable Sys Apps, and Switch Launchers with One Tap:

[FireOS 5.x + ROOT] Quickly switch to Amazon UI and back: http://xdaforums.com/fire-hd/general/fireos-4-5-x-root-quickly-switch-to-t3145613

Get Wallpaper on OS 4 Custom Launcher

[HOW TO] Get Wallpaper on Custom Launcher: http://xdaforums.com/fire-hd/general/how-to-wallpaper-custom-launcher-t3123009