I bought a lot of things on the express, and there are many short messages on my mobile phone. Is it better to delete them all or take them away?

There's no need. Keep them all, because text messages will take up your memory. If the courier has been received, it proves that the transaction has been reached, so you don't need to keep it. And you also have an order on the app software. You can still find it if you want to inquire.