ElJugador: I am a paladin so how should i level up
If you mean how as in "what to click", when you reach enough experience for a new level, your character portrait will change into a sort of static "bubbling" picture. Click on that; go through the lists.
If you mean how to build the character, that depends on what type of paladin you're aiming at. If you're going sword-shield-heavy armour for example, Exotic Weapon Proficiency so you can use a Bastard Sword, Weapon Focus for same, Power Attack, then Cleave (if Paladins can get Cleave; can't remember) is a valid starting point.