When you reach level 45 on Console or level 133 on Steam (as of Patch 2.6.2, released on September 1, 2014), you will be given the option to Prestige after finishing a match. This will reset your Player Level to Level 1 on Consoles, or Level 16 on Steam. This puts a special badge next to your Steam username on the Leaderboards, the Main Menu, and the in-game Scoreboard, differentiating you from newer players.
Since Prestiging resets your level, you will have to unlock the upgrades for every Awesomenaut all over again. Maps and 'Nauts will remain unlocked even after you prestige, however.
- If you refused to Prestige, then the game won't ask you to Prestige again. This can be changed by going to the in-game Options and checking "Prestige", which will allow you to Prestige after a match.