change default printing settings

Solution 1:

You can use Cups administration page. You can access it by opening http://localhost:631 in your web browser.

Then select Administration -> Manage Printers

Select your printer and then, on the "Administration" dropbox choose "Set Default options". Change the default settings and finally press "Set default options". If it asks you the username/password use the same combination you use to login.

Solution 2:

Via Ubuntu settings

On Ubuntu 20.04.1 LTS the settings can normally be set via

Settings --> Printers -->

But they don't always seem to take effect or perhaps there is another configuration conflicting which takes precedence.

Via CUPS server

Salem in his answer describes how to access the CUPS server via web-browser.

This server can also be accessed under

Settings --> Printers --> Select Additional printer settings

A GUInterface of the connection to the local host server will appear

Right click on the printer of interest and select properties, etc, etc..