I followed this Q&A for Ubuntu Server only: How can PPAs be removed? and used one answer there:

sudo add-apt-repository --remove ppa:whatever/ppa

...but it only worked for the current session and didn't survive a reboot. In other words the PPA reappeared later. This made a Graphical User Interface (GUI) method that "simply works" with the click of a button highly desirable.

How can a PPA be removed with the GUI?

This is not a duplicate

This is not a duplicate of: How can PPAs be removed? where only answers using the terminal are requested. Answers using the GUI have been deleted. The rules can be bent when a terminal answer is given followed by "you can try this GUI option too".

This question is about Ubuntu Desktop and GUI answers are requested. A new GUI solution in the future should be deleted from the Ubuntu Server question but is allowed here.

Solution 1:

Remove PPAs with Ubuntu 16.04 LTS GUI

Select Software Settings -> Software & Updates -> Other Software:

Highlight the PPA you want to remove and click the Remove button.

Note that many PPA's have two entries; one for the programs and one for the source code.

You should have an Internet connection before completing this operation because Ubuntu needs to update apt sources when you close the panel.

For more details see these Tecmint Instructions with many screen shots for both adding PPAs and removing PPAs.

Solution 2:

I found better method.
We can use Y PPA Manager for installation and removing software:

sudo add-apt-repository ppa:webupd8team/y-ppa-manager
sudo apt-get update
sudo apt-get install y-ppa-manager

It has Purge button under Manage PPAs menu: