To make dist upgrade from Sparky 5 to 6 do:

1. Backup your personal files to external disk or partition.

2. Change Debian repositories from buster to bullseye at the file:

 /etc/apt/sources.list

So it should look like that:

 deb http://deb.debian.org/debian bullseye main contrib non-free
 deb-src http://deb.debian.org/debian bullseye main contrib non-free
 deb http://security.debian.org/debian-security/ bullseye-security/updates main contrib non-free
 deb-src http://security.debian.org/debian-security/ bullseye-security/updates main contrib non-free
 deb http://deb-multimedia.org/ bullseye main non-free

3. Change Sparky repositories from nibiru to potolo at the file:

 /etc/apt/sources.list.d/sparky.list

So it should look like that:

 deb [signed-by=/usr/share/keyrings/sparky.gpg.key] https://repo.sparkylinux.org/ core main
 deb-src [signed-by=/usr/share/keyrings/sparky.gpg.key] https://repo.sparkylinux.org/ core main
 deb [signed-by=/usr/share/keyrings/sparky.gpg.key] https://repo.sparkylinux.org/ potolo main
 deb-src [signed-by=/usr/share/keyrings/sparky.gpg.key] https://repo.sparkylinux.org/ potolo main

4. Refresh package list:

 sudo apt update

5. Install sparky-apt_YYYYMMDD~sparky6 & sparky-core_6.YYYYMMDD packages which have to remove sparky5-apt:

 sudo apt install sparky-apt sparky-core

6. Refresh package list again:

 sudo apt update

7. Dist upgrade now:

 sudo apt full-upgrade

If any problem run:

 sudo dpkg-reconfigure -a
 sudo apt install -f