Advancement rules from the published version:
At each level, the player does the following:
• Adds a number of stamina points to her dog’s maximum total, based on her character’s calling
• Gains another stamina die
• Spellcaster characters gain two additional spell slots (plus another one if their Constitution modifier increases)
• Spellcaster characters choose two more spells (p. 101)
Every two levels, the character’s proficiency bonus also increases by one.
The character also gets one improvement each level. This can be any of the following:
• Increase an ability score by 1 up to a maximum of 20. Also, take a new skill.
• Take a new calling, breed, or aptitude trick.
• Refine an existing calling or masterwork trick.
(I can't remember if refinement was in the Early Access rules, if not, hit me up)