The phone is running:

SM-G390F

Android version : 7.0
Baseband version: G390FXXU1AQI2
Build number    : NRD90M.G390FXXU1AQI3

Root Device

• Download Boot & Recovery image from CF-Auto-Root for this device: ​https://desktop.firmware.mobi/device:289
• Enable 'OEM Unlocking' in 'Settings -> Developer options'
• Reset device to factory default
• Put device in Download Mode by Powering it while holding down this keys: Power + Volume Down + Home.
• Retrieve PIT or download attached file sudo /usr/local/bin/heimdall download-pit --output SM-G390F.pit
• Use Heimdall to install new images: sudo /usr/local/bin/heimdall flash --pit SM-G390F.pit --RECOVERY recovery.img --CACHE cache.img
• Reboot phone and rooting will be done automatically

Removing factory applications

I do not like all Samsung and Google Applications which comes by default with the phone. It collects too many data, runs in background consuming CPU, memory and thus battery power consumes storage space.

• Disable 'Play Store' automatic updater
• Disable all applications which are not needed. Restoring their stock versions if needed.
• Use a Application called ​Applications Info located in ​F-Droid package manager to find locations of applications to be deleted.
• Delete using CLI: $ adb shell $ su $ mount -o rw,remount /system $ rm -R /system/app/application-to-be-removed $ rm -R /system/priv-app/application-to-be-removed

file:/system is read-only be default. use mount -o rw,remount /system to make it writable.

Original firmware

Can be found at ​http://samsung-updates.com/device/?id=SM-G390F