Recommended migration strategy from buster to bullseye

I use Seafile on RPi. I have successfully upgraded Seafile to version 9.0.2 on buster.
What is the recommended migration strategy for upgrading buster to bullseye?
Esp. since there now is a dedicated package for buster and bullseye.

My current RPi version:

$ cat /proc/device-tree/model
Raspberry Pi 2 Model B Rev 1.1

Thankful for any pointers!