I had the same problem before kasi nagpadala yung tita ko ng phone na locked sa AT&T tapos I got help with my SIM Network Unlock Pin. Now, I could use it to any network here in PH.
I have a Samsung Galaxy On5 and I followed this:
Enable the unknown sources in setting menu.
Settings > Security > Unknown Sources
Download KingRoot.apk file into your device.
By the time download finish, install and launch Kingo Root.
Press "One Click Root" when you see the button.
Wait until...