Advancement takes place after you collect enough experience to reach another level within a Tier. Once that happens, you will be able to hit the plus button on your character's screen and select one of four options:
- Increase your stat pools.
- Increase your stat pools' Edge (free Effort).
- Increase your max Effort.
- Gain a new skill or improve one you already have or improve one of your active abilities.
Each of these options can be selected once per Tier. Once all four are exhausted, you reach the next Tier and you can select them once again, except this time, you will gain new abilities and skills.
The highest Tier possible for any character in the game (due to hard cap) is 4; after getting all 4 Steps in Tier 4, further XP gains doesn't give any actual benefits. For the protagonist, that's likely to happen late in Bloom, if all sidequests and XP dialogue options are chosen.