From now on, the integrity of the system is not guaranteed in case of stability, performance or safety failures. The Debian LTS team will continue to maintain Debian 8 until June 2020, but will only release patches for the vulnerabilities they consider most critical.
To update to the most recent version, Debian 9.4, it is first recommended to perform a system check to eliminate obsolete packages that may create problems during the update process. Simply start your terminal and execute the command aptitude search ‘~ o’.
The next step will be to proceed with the update. To update the repositories, applications and packages of the distribution we will execute apt-get update, apt-get upgrade and apt-get dist-upgrade.
Once this is done it is advisable to execute a series of commands to verify that you have all the packages installed and thus move the software repositories from Jessie to Stretch: dpkg -C, sed -i ‘ s / jessie / stretch / g ‘/etc/apt/sources.list and apt-get update.
After following these steps you just need to restart the system to start using Debian 9 Stretch, which will have basic support until 2020 and extended support until 2022.