Spend 50 Attribute Points.

You receive an Attribute Point when you Level up by feeding Vulgrim the souls you collect from defeated enemies and breaking certain objects. You can either choose to add it to HEALTH, STRENGTH or ARCANE when you press 'VIEW'.

Also, Luminous Visage can be found scattered around the areas as well as being picked up after defeating the Sins. They will level you up instantly without the cost of souls. It will be in your inventory if you have one; just press and hold 'A' to shatter.