You need to be Transcendent Class to unlock T2 runes eg High Wizard.
Speak to Orloum to start the unlocking quest. She will task you with killing 50x Orc Archers and providing 15x Nibelungen Shards (Guild Valhalla Raid Reward).
Once complete you will have access to the extended rune grid which includes additional spells like Meteor Storm.
Looking to unlock Aesir T1?
Where to Find Orloum
Prior to Episode 5 Orloum the Aesir Monument NPC could be found in the Guild Hall. She has since been relocated to Prontera (See Above).