If your sources file references the release name (e.g.:bookworm), you change them to trixie, then “apt update && apt dist-upgrade”.
or,
If your sources file directly reference distro-suites (e.g.: stable), you just “apt update && apt dist-upgrade” since stable is now pointing to trixie.
In the first reboot, you run “apt autopurge” to remove packages which are not needed anymore.
