Please note that the current version of bookworm.
Also, the creators of the Raspberry Pi usually recommend a clean installation if the Debian base system is being updated.
Proofs here
How do I get it?
With a major upgrade, we recommend downloading a new
image, reinstalling any applications, and moving your data across from
your current image. Debian major version upgrades contain a lot of
changes, and it is very easy for some small tweak made somewhere in
the system to be incompatible with some change you have made, and you
can end up with a broken system and a Raspberry Pi that won' t boot.
The easiest way to create a new SD card is with the Raspberry Pi
Imager tool available here, or you can download the new image from
here and use a tool like Etcher to flash it to a new SD card.
If you really want to try upgrading an existing image, there are some
instructions on the forums here – but we don’t support or recommend
this, so be warned: you are on your own if anything breaks! Make a
backup of your SD card first so you can always go back to a working
system if you need to; the SD Card Copier application in Raspberry Pi
OS is a good tool for this.
As ever, your feedback on this release is welcome – either add a
comment below, or head to our forums.
If you decide to upgrade anyway.
To delete the local package cache.
sudo apt clean
In addition, you can remove unused dependencies that were once automatically installed.
sudo apt autoremove
Also, if the system has been running for several years, it may be useful to vacuum the system log.
Leaving only the last 5 days, for example. You can choose the number of days yourself.
sudo journalctl --vacuum-time=5d
