"What things change" — well, lots of them. Different programming languages, different architecture that leads to different approaches, and so on. So be ready to re-learn many things.

There's an article specifically aimed at the Solidity developers, probably it's a good idea to start with that: https://blog.ton.org/six-unique-aspects-of-ton-blockchain-that-will-surprise-solidity-developers

And after that... just go through the basic TON stuff, I guess — documentation, tutorials and so on.