There is no trial version for the application. You have the option to install the Starter Edition and then upgrade to full version of the software for 70 $, as you can see in the image. You can download the starter version and use it accordingly without expiration date, but it will miss some features.
The update is done in the application, if you plan to buy it.
Download free (aka Starter): http://www.serif.com/free-video-editing-software/