[Upgrading, Modifying and Unlocking] Juangiluruguay:
Ok guys, I see that this tread is for the rom but many have rooting issues.

I will tell you my experience.

After searching all over internet, I used 1 method to root ( from prydmus), and it was to install Magisk manager in the phone, and DOWNLOAD a custom bootloader image to the telephone internal memory via SP FLASHTOOL.

It DID ROOT MY TELEPHONE.

Second, I installed TWRP 3.1.1 with a method written by 'Razaaq' but.... instead of selecting DOWNLOAD ONLY, I selected INSTALL!!!, very important!!!!, otherwise you have to start giving fastboot or ADB commands.... too complicated.....

Besides, if you screw up with wrong TRPW... as happened to me when tried to use the TRWP APP... I bricked my phone... and I brought it back to life flashing via INSTALLING and NOT DOWNLOAD ONLY.... and my phone started...

Now.... to boot in TWRP.... just have to install an APP like QUICK REBOOT.... works good for me!!! giving commands via PC... don't like it...

TIPS... Get the good DRIVERS and set your telephone to usb debugging, and whatever else you might want...

In My telephone I found something about to let the Phone Boot to be Unlocked.... I just allowed it too..

USE WINDOWS 7 !!!! ... At least I did after doing some readings... to make things more secure.

Connect the telephone AFTER you press the DOWNLOAD BUTTON in SP Flash Tools, because the telephone will listen for communication for couple of seconds only.... otherwise you will have to re start... (this is for using flash tools..)

Again... Drivers.... I installed ADB, Fastboot, and the ones for MT65XX Vcom Drivers.....

You can open device manager and check what happens with the device when is connected.

It should show.... ****.. I forgot... but is something related to the MODE of listening and will be in and out very quickly...

If you disconnect and connect again, you might not see it again being displayes as a new hardware " on for a couple of seconds and off", so.. you have to reboot.

When I got that error of preloading... i tried other drivers, but.. the thing... I believe.. was that I had to reset to try again a new connection, and press DOWNLOAD BEFORE I connected my phone.

Just read this all and hope it makes sense to most, otherwise, prepare all this steps before you attempt to ... get it right????

One more thing for the unexperienced ones... like me...

Choose the right NAMED SCATTER file, I mean, with your specific device. Mine, according to banggood was 6750, and not 6755...

For Bootloader.img, make sure you ONLY Select (tic) Bootloader.img and have it in the right folder selected.

For Recovery.img, make sure that it is the name, and rename what is most likely you are going to find with a recovery(1).img, otherwise the program is not going to recognize that (1).

Remember to INSTALL recovery.img..... not just... DOWNLOAD ONLY.

I gave up with trying to boot with buttons. The boot app works just fine.

What else..... dont try to boot with the APP, if you didn't succeed flashing it right.

In both cases you will see a popup saying it went well.

When you are rooted, the telephone will immediately let you know when you boot

The telephone should be rooted and with TWRP installed.

Back up and play with different roms, and.... pray to the god on watch and...

Good luck