Update RNEG2.70.E.3 to higher?

Hi.
I've got a C5 Tourer 3/2013...do someone know how to update the firmware?

Latest version is 2.86.B.1 (APV 9691894880) available by your dealer, but why do you want update if your system works, there's no much improvement or new functionality.

mytheuzen wrote:Latest version is 2.86.B.1 (APV 9691894880) available by your dealer, but why do you want update if your system works, there's no much improvement or new functionality.

First of all, thanks for your answer!
I found all the version from 2.71 (my version is 2.70.E.3) till the one you wrote. Anyway it was impossible to update for me....
I tried to do one by one (they're 6 versions in total) or directly to the last one but after the media control (about 5 minutes) the response is always "update not complete or corrupt".
I'd like to update because the phone section is very slow and, in my opinion, is incomplete (for example the dial part) and, anyway, I hope there are improvement in general.