I have previously installed node 1.33.0, and now I've upgraded my node to 1.35.0. I already have a 'db' folder when I'm using 1.33.0. If I want to switch to Preview / Pre Production configuration and environment, should I create a separate 'db' folder and download the full blockchain from the beginning, or can I use my previous 'db' folder from the Legacy Testnet? Will it cause any conflict?
First, you need to upgrade to 1.35.3 for Preview or Preprod. You will need the new configuration files for Preview or Preprod (https://book.world.dev.cardano.org/environments.html), and you need to delete the db folder and sync from scratch (which is very fast now, as the blockchains are small).