There are 8 of them in total. To unlock the advance classes, you need to level up the other classes to a certain level for them to show up in the class changing option when you talk to Chat. The advance classes require certain amount of grade points. You only need to pay the grade points once for every advance classes.

Unlockable	How to Unlock
Bishop	Cleric and Wizard Lvl30, 500GP
Dual Fencer	Fencer Lvl15, 200GP
Large Fencer	Warrior Lvl15, 200GP
Magic Fencer	Warrior, Fencer and Wizard Lvl30, 500GP
Monk	Cleric and Grappler Lvl15, 200GP
Ninja	Fencer, Grappler and Hunter Lvl30, 500GP
Paladin	Warrior, Cleric and Large Fencer Lvl30, 500GP
Pirate	Thief and Hunter Lvl15, 200GP