Unlocking the bootloader
For this whole guide, you will need the following requirements:
- A Windows PC (Windows 7 or higher).
- A supported Lumia phone.
- 8 GB of free storage on the PC.
- 6 GB of free storage on the Lumia.
- Windows Phone 8.1 or Windows 10 Mobile (1607 or older) installed in your Lumia.
You need the following programs/resources:
Now, extract and open WPinternals. Remember to extract all files in the zip to the same folder. The program will not work properly if a file is missing.
Carefully read through the Getting Started page.
On the Lumia, boot into Windows Phone. Connect the device to your computer, your phone information should appear in the Info page.
Go to Download page. In the Model section, click Search, then Download all.
In case you are unable to download, or the download is too slow: LumiaFirmware
Go to Unlock bootloader page.
Donor FFU
Visit LumiaFirmware, find an FFU that has a supported version showed in Getting started (it could be other phone FFUs).
Pick Lumia 950 or XL with version 10.0.10586.318 for good results.
Click Unlock. The unlocking process will reboot your phone many many times, do not disconnect the phone. Wait until it shows "finished".
Wait for your phone to boot back to Windows Phone. After that, go to Manual mode, then select Switch to Mass-Storage-mode.
Your phone's screen should appear black right now. MainOS drive should appears in File Explorer. At this point, you are ready to move on to the next part.