Ok, so the first point you can get this is after defeating the First Warden.
A checkpoint/floaty red spinny thing(!) will appear in the middle of the room and explain the upgrade system to you.
Hit backup to enter the upgrade system, and then pull RT or LT to add your XP to either attributes or spells. I went for attributes, and when I filled the first bar (just hold down RT) I got an attribute and the acheivement. You will have enough XP after defeating the First Warden to get a attribute point upgrade.