Ubuntu 12.04 LTS includes an old version of phpmyadmin so I was trying to figure out how to upgrade it.

The following PPA is the one to add:

ppa:nijel/phpmyadmin

see https://launchpad.net/~nijel/+archive/phpmyadmin?field.series_filter=precise

but I could not get the command add-apt-repository to work

The following page http://ubuntugeek.com/forum/index.php?topic=4196.0 has a command to fix this:

apt-get install python-software-properties

once this command has been run then add-apt-repository ppa:nijel/phpmyadmin will work!

Once the command has been run then the phpmyadmin package will get automatically included next time you run the package updates.

Finally I noticed that there were some errors showing when trying to browse any database.   This can be fixed by importing the following file, using the "import" tab in phpmyadmin.

/usr/share/doc/phpmyadmin/examples/create_tables.sql.gz

When selecting the import tab I made sure I was in the "home" screen rather than selecting an existing database.