Debian 10

The procedure is as follows :

Backup your system.
Update existing packages and reboot the Debian 9.x system.
Edit the file /etc/apt/sources.list using a text editor and replace each instance of stretch with buster.
Update the packages index on Debian Linux, run : sudo apt update
Prepare for the operating system upgrade, run : sudo apt upgrade
Finally, update Debian 9 to Debian 10 buster by running : sudo apt full-upgrade
Reboot the Linux system so that you can boot into Debian 10 Buster
Verify that everything is working correctly.