How can I update to GDR2

I have a 920 that in Build 8.10.12393.890. I want to install W10M to it but as you can see I can't. So I need to update it to GDR2, but how? I tried the tutorial on W10M Group Youtube Channel but it didn't worked and give error code 0x80188306. What can I do? I really love this phone, I wanna install W10M to it.

Product Code: 059S5C9
Bootloader is not unlocked and the other things are in stock settings.