Upgrading to the latest version of Zoneminder (currently 1.26) is a simple process of executing the following commands in the specified order:

sudo apt-get update
sudo apt-get upgrade
sudo apt-get dist-upgrade
sudo apt-get install python-software-properties
sudo add-apt-repository ppa:iconnor/zoneminder
sudo apt-get update
sudo apt-get dist-upgrade

The last command above will prompt you several times for the ZoneMinder upgrade.  Answer in this order: Y,Y,Y, Enter, Enter, Y,Y
Ignore the warning about stopping Zoneminder as it will already be stopped.

If you’d like to see the Zoneminder upgrade process looks like and how I answered the interactive upgrade questions, click here.

Important: Sometimes Zoneminder upgrades will destroy your symlinks.  Perform the following commands to reestablish these symlinks:

sudo /etc/init.d/zoneminder stop
sudo ln -s /var/cache/zoneminder/events /usr/share/zoneminder/events
sudo ln -s /var/cache/zoneminder/images /usr/share/zoneminder/images
sudo /etc/init.d/zoneminder start

Lastly, after the upgrade there’s a chance your Zoneminder won’t automatically start.  To fix this:

sudo nano /etc/init.d/zoneminder

Add “sleep 15″ before the zmfix -a line as pictured below (see arrow) and reboot.

You can upgrade to future versions by simply typing the last command (sudo apt-get dist-upgrade) as you have already added the repository for ZoneMinder.  Just make sure to add the sleep command above when upgrading.