Here is the official Season 9 Character Conversion document, but here are the important parts…
Advancement Checkpoints: Gone. You MAY gain a level for any character that had any unspent.
Treasure Checkpoints: Spend them if you want, but no more Treasure Points. Yay! See Magic Item limits in our previous article: Official Season 9 AL Rules! Magic Items, Gold & Leveling!
What if my character has more Magic Items than my Tier limit? Choose the ones you want to keep, up to your Tier limit. When you go up to the next Tier, you can re-add one of those items back to your character. Reasonable.
What if my character has FEWER Magic Items than my Tier limit? You get more! Choose a number of permanent magic items from those that the character unlocked by adventuring up to your character’s limit. Very reasonable.
What if my Tier 3 character (or below) has Legendary Items? Only allowed for Tier 4, but items are “held in reserve” and may be reclaimed once the character reaches Tier 4. Fair.
What about Magic Items with Persistent Effects, ie. Tomes of Understanding, Manual of Golems, etc.? They DO count towards the Magic Item Tier limit. You MAY remove them and their effect if you desire. Common sense, nice.