Here's the official list:
Apprentice 0
Messenger 25
Town Crier 75
Scribe 150
Narrator 200
Linguist 275
Bard 325
Chronicler 375
Philosopher 500
Sage 1000
As for when you can change your rank title, we reserve that for FanPlay and OtakuDuet staff only. Staff include forum moderators, so if you spend alot of time on the forums and we like you =P you get moderator status and your own happy rank.