When you are about to upgrade ZendTo using either the command
sudo apt-get upgrade zendto
yum update zendto
there are a few files you may want to save first, in case your configuration changes get overwritten by mistake when upgrading the package.
The files to save out of the way are as follows:
Note that all of these files are intended for you to modify if you wish to, and they are all marked in the packages as being "configuration files" that should not be overwritten during an upgrade. However, particularly when using Ubuntu, it is very easy to accidentally overwrite them with the unconfigured new version of the files. So this is just to be extra cautious.
There are tools /opt/zendto/bin/upgrade_preferences_php and /opt/zendto/bin/upgrade_zendto_conf which will copy your existing changes to preferences.php and zendto.conf into the default new one supplied with the upgrade.
Just run either of the tools on their own to see how to use them. Always tell them to send the output to a new file (after the ">"), not to your existing preferences.php or zendto.conf file!