First you have to collect 1x Magic Powder, in RaidBox Act 3, to exchange them for 1x Prestige Item, in Act 3 NistroVille.
After you use this Item, your Character gets Reset to Level 100, HeroLevel 1. With the difference of having x2 Permanent Buff!
You can do this up to 3 times right now.
Requirements to use the PrestigeItem and Buff-Effects are:
Herolvl 150 For Prestige 1
Herolvl 200 For Prestige 2
Herolvl 225 For Prestige 3