W10M isn't officially released OTA yet . You can get the W10M build via Insider program at your own risk or wait a little more .
P.s current build works well on 520
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We don't have any official dates for Windows 10 Mobile rollouts. Stay tuned to our News Blog. They will shout out all OTA rollouts as they happen by model and country. Our members are great, many spotters will report in on conditions.