Before doing an update on your Cloudlog-installation please make a backup of your existing installation. During the update-process some configuration-files could be reset to defaults so you have a backup to reenter your settings into the new configuration-file.

One way to update an existing installation of Cloudlog is to download the https://github.com/magicbug/Cloudlog/archive/master.zip and copy it's content over the existing files (after doing a backup as mentioned above). Second step would be to take a look at your old application/config/cloudlog.php and compare it with the actual one to enter your changes back into this file.

Another way (and in my eyes the way you should prefer) is to issue the git pull-command and update it via the git-mechanism. Here you should also create a backup before. Second step here would also be to take a look at your old application/config/cloudlog.php and compare it with the actual one to enter your changes back into this file.