[Galaxy S 5 Q&A, Help & Troubleshooting] ranthon007:
How to Downgrade Firmware on AT&T’s S5 Active SM-G870A and get Root Access after Augu

It took me over a week to search through threads and learn how to root my S5 Active SM-G870A after I installed the new August 2014 update and then later discovered the SD card issue (i.e. needing root access to allow apps to write to it).

Anyway, these forums helped but I had to piece lots together in order to do it right and make sure that I was not going to destroy a $600 phone.

Below is a compilation of what I found. I do not take any credit for the original contents. I have simply organized what I have found in many other threads so that others searching to resolve the same issue can do so in less time than me. Also, I put this together so that I do not feel like my time was wasted hunting all of this down!

How to Downgrade Firmware on AT&T’s S5 Active SM-G870A and get Root Access after August 2014 Update

Step 1: Downgrade your Phone’s Firmware to an Earlier Version

Original Thread Link: http://xdaforums.com/showthread.php?t=2799754

Before Starting:

1.	Download and Install the latest Samsung USB Drivers.

2.	Download and install the latest version of Odin (you may need to extract it using a zip program).

3.	Download and extract the firmware file: http://www.sammobile.com/firmwares/3/?download=31669 (May 9th, 2014) OR HERE.

4.	Make sure USB debugging is checked under “Settings/Developer Options” (If you don't know how to do that, go to "About Device" in Settings, and click on "Build Number” 5 times to unlock “Developer Options").

5.	Back up your phone using any backup program that does not require root, just in case.

Flash Instructions:

6.	Open Odin v3.09.

7.	Reboot phone in Download Mode (press and hold Home + Power + Volume Down buttons).

8.	Connect phone to your PC and wait until you get a blue sign in Odin.

9.	Add the un-zipped firmware file to AP / PDA (Make sure re-partition is NOT ticked).

10.	Click the start button, sit back and wait a few minutes.

You should see a bar at the bottom of your phone indicating progress and also in Odin. Once the phone restarts Odin will check to see if the firmware flash was a success. If it is, the “System” box will now display “Success.” Congratulations, you have downgraded your phone’s firmware, now you can root it using towelroot (www.towelroot.com).

Step 2: Install Towelroot

Before Starting:

1.	Disable antivirus software on your phone. Towelroot is an exploit: it is how you get root. So your antivirus (if it’s worth a damn) will flag it.

2.	Make sure that your phone can install application from unknown sources: Settings>Security>Unknown Sources>Check.

Towelroot Instructions:

3.	Using your phone’s browser navigate to www.towelroot.com.

4.	Click on the lambda in order to download the tr.apk file.

5.	Locate the file on your phone and click on it. Chose the Android Package installer.

6.	Follow the additional instructions.

Step 3: Do I have REALLY have Root Access?

1.	Go to the Play Story and search “root checker.”

2.	Download and install the app with the same name.

3.	Run it. If it is a success, then download and install SuperSU.

I recommend getting Titanium Backup and paying for the pro-version ($5.99). Doing so will allow you to disable the AT&T notifications (“Freeze” AT&T Update) that will bug you once you downgrade your firmware, and there are lots of other things you can do with it now that your phone it rooted.

This “complete” intro guide should help anyone (especially newbies) root their S5 Active SM-G870A in a safe way if they have upgrade their phone in August 2014 or after.