z3 d6616

Hello,
Today my phone arrived from ebay but I can't update it to marshmallow. My phone version is d6616. I have been reading that this phone is from T-mobile (dunno what that means) and that it won't get updated by them.

So can anybody help me. If somebody know the way h2 root and that stuff since I don't. If someone is nice and want to help me to update my phone, just provide me steps.

Hope I don't ask to much.
Hoping that I'd get answers here.

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