At what level can I Advance (class upgrade)?

You can select your Advancement during the initial character creation process.

Afterwards, upon reaching level 50, players may perform the 1st Awakening for their class.

The 2nd Awakenings are accessible upon reaching level 75.

Finally, Neo: Awakenings that are accessible upon reaching level 100.

For example:

Male Gunner > Ranger (at Lv. 1) > Desperado (at Lv. 50) > Raven (at Lv. 75) > Neo: Ranger (at Lv. 100)

Female Fighter > Nen Master (at Lv. 1) > Blazing Flower (at Lv. 50) > Nen Empress (at Lv. 75) > Neo: Nen Master (at Lv. 100)