[Miscellaneous Android Development] antoniu200:
So, I'm yet another one who's asking for help. Not because I can't flash a ROM, but because I have never used this program before and I really don't have the time to explore and explain to myself what this and that setting does. So, by replying to this thread, you would do yourself a favor (not getting any more notifications from people in this thread trying to figure out how it works) and me and much more guys like me (by telling us how it's done, since there are no other places on the Internet regarding the root of this phone).

EDIT: I figured it out, after 2 hours.

So, here we go:

Before you start this, make sure you have the LG drivers installed! If not, connect the phone to your PC and in the notification center, select the notifiaction that says "Device connected as ___". It will open up another window. Press on the three dots in the up right side of the screen and select "Install drivers", if the phone doesn't ask for this as soon as the window is opened. The driver installer should pop in your computer. I guess you know what to do with what popped up.

1st: Create a Mega account, if you don't already have one, you'll understand later why. Download and extract the ROM that the OP is giving link to. If you're using Firefox, get Chrome and download it from there as the file is hosted on Mega, which won't store almost anything if on Firefox. So, open the ROM link in Chrome and log into your Mega account. Now, open the link again, right click on that folder and select "Download as .zip" file. Chrome should ask for permission to let Mega store things on your PC, allow it.

2nd: After the download is ready, extract it somewhere you won't forget it's there.

3rd: Download Smart Phone Flash tool. Select last version compatible with Windows PC and, after it's downloaded, extract it. Right click on flash_tool.exe, go to compatibility tab and select "Run program as Administrator".

4th: Download Scatter file - right click on the attached file to this thread and select "Save as…" and click OK. The file should be saved in your Downloads folder.

5th: Open flash_tool.exe and go to download tab. Select "Scatter-Loading" and point to the file downloaded at step 4. VERY IMPORTANT!! DON'T MODIFY ANYTHING!! LET EVERYTHING AS THE PROGRAM SEES AND CONFIGURES IT!!

6th: You will see that only "system" is checked, but it isn't pointed to any file. Under the directory tab, you'll have to click on the empty space and point to where you extracted the ROM, at the file system.img.

7th: If your phone is on, turn it off and remove its battery.

8th: In flash_tool, press download. Now, connect your device to the computer and do a short "Volume Up" button press. The program will detect the phone and it will start the flashing process, which will take ~5 minutes.

9th: After the flash is done, you can close the program and disconnect your phone. Plug the battery back in and power the phone back up. After it boots up, you may get com.android.phone errors or something similar. You will have to get to Settings-Backup&Reset and reset the phone. After it's been reset, you will be able to enjoy your rooted LG K4. Good luck!

Thank you, OP for this thing. Also, some extra information, this is ranked as "Hard" to root phone by Root Checker and it is ~4600th hardest to root out of 5600 phone model numbers registered in Root Checker. Didn't expect that.