The easy way
Whilst changing the timezone of a machine once it has been installed is not a very common job it does seem to be something that many people struggle with.
When it comes to Debian systems the simple way to edit your timezone is to use the /usr/bin/tzselect command.
The tzselect command will prompt you for your region and then offer you a list of cities within that region.
For example selecting “Europe” from the available regions will present you with the following list of available cities to choose from: