If you are using the Enigmail security add-on for Mozilla Thunderbird under Ubuntu Linux, you may have recently discovered (as I did today) that it no longer works with the version of GnuPG that you have installed, and that you need to upgrade. But it’s not evident how to do this, as there is no GnuPG update available in the Ubuntu Software Center.
Fortunately, there is an easy way to upgrade Ubuntu to GnuPG 2. Just open a terminal and type:
sudo apt-get install gnupg2
and enter your password when prompted.