how do i change my main class

[Izularia]

Once you reach level 10:
-Go to the City which is home to said class you want to change to.
-Talk to the receptionist of said class' guild twice.
-Complete the quest.
-BINGO

I don't think that's what they have asked.

OP, go to your Control Panel and then to "Edit Character", there you can set your main class.