What is the correct way to upgrade Debian 8 to 9?

Question

Debian

Hello!
It's about the server.
Now stands Debian Jessie.
Previously, when a new version of Debian came out, I deleted everything, installed a clean OS, and reinstalled packages (php, nginx, mysql, ...). Because I thought that it would be better this way, there would be no garbage from the old version.
Accordingly, 3 questions:
1. How to update correctly? Should I wait until Debian Stretch is stable and just do apt-get update && apt-get upgrade && apt-get dist-upgrade ? Or in any case, the distribution will not be updated until I write in sources.list instead of jessie stretch?
2. How clean is the update or is it still better to install everything from scratch?
3. When can we expect Stretch to be released?
Thank you!

Answer 1

1. There are two types of naming distributions in sources.list:
   a) by name: stretch, jessie, wheezy; b) by status: sid, testing, stable, oldstable;
   If a name is specified, then the change of version statuses will not affect in any way, the system will only grow old. If a status is specified, then when changing statuses (accepting a new version), a jump to a new version will occur, after which the system will age until a new jump to a new version.
   
2. Which is better is individual. Those who are afraid of losing some of their settings prefer updating. Those who are afraid to drag their crooked settings into the new system should start from scratch.
   
3. It has been in full freeze since the beginning of February. Usually, a little more than six months pass from the moment of freezing to release.
   

Answer 2

Debian has instructions on how to upgrade . Everything is step by step.
Nothing significant changes from year to year.