Each time your character levels up, you must update their stats to reflect their new level.
Depending on your level, you qualify for bonuses when you level up. The class level table outlines the following benefits which you receive at various levels:
In addition to the bonuses above, you also gain (2+Int) Skill points per level. You also roll your hit dice and add the result to your total hit points, provided you have not exceeded level 12
Ability score increases and hit dice must be spent when you receive them, all other bonuses may be saved and spent later if you wish