Here's some points what will be happening with ethereum after the upgrade

1. Scalability increase
2. Merge chain
3. shard chain upgrade

What you need to know if ethereum blockchain 1 and 2 will be merged into the one blockchain. I suggest you to read more about that through this link https://ethereum.org/en/upgrades/

You will be getting a lot of knowledge about what will be done after the upgrade and what things that will happen with ethereum blockchain.