the RCD 510 is a different device made by Blaupunkt, the RNS 510 is made by Continental. they look almost the same because that's what VW wants. the hardware is totally different and the RCD 510 has an internal 6x CD changer. if there's no option to change the language in the device settings, then you can't do it.
also, there are at least 3 different versions (Europe, US, China) of the RCD510, everyone with its own disadvantage if used in another market (e.g. no RDS, not all frequencies, not all languages etc.)
i can't find the thread you're talking about but if a dealer did it, then it's possible with either VAS or VCDS. VAS is the official workshop software, VCDS is for anyone to buy. why don't you just go to your dealer if you already know about it?
Latest software update for RCD 510 solve few problems, mostly with Bluetooth, is for all previous "software levels" 0007, 0008, 0009, 0010, 0011, 0012, 0013, 0014, 0015, 0016. Dont know whats the lastest version number, but this is from VW upgrade manual, released 11.1.2013, which someone scanned on web. This mean that was released more than 10 updates for european version. And you do not need be hot head, forum is to help from/to people who knows... Even if you cant find some, which is possible find by Google per 10 seconds, man...