When you reach level 15, you may get promoted in Job Center (402,369). After promotion, you will get a new title and more attribute points, and learn elementary skills.

Go to find corresponding NPC who is responsible for your promotion:

Warrior God:
Promote Warrior and teach Warrior skills.

Archer God:
Promote Archer and teach Archer skills.

Trojan Star:
Promote Trojan and teach Trojan skills.

Taoist Moon:
Promote Taoist and teach Taoist skills.

When you reach higher level, you can get promoted again. After promotion, you will get a new title and more attribute points, and learn new skills.