First decide which version of Debian you wish to upgrade to. The versions of Debian currently supported are as follows:
|Version||Code name||Release date||End of life date|
|Stretch||June 17th 2017||approx. 2022 (LTS)|
|Jessie||April 25th 2015||~June 6th 2020 (LTS)|
|Wheezy||May 4th 2013||May 2018 (LTS)|
Information on upgrading Debian 6 Squeeze to Debian 7 Wheezy can be found on the web page accessed using the URL as follows:
Information on upgrading Debian 7 Wheezy to Debian 8 Jessie can be found on the web page accessed using the URL as follows:
*** Note: Although it may be possible, it is not recommended to even attempt to do upgrades to a more than 1 version higher.