It depends on how the short code was defined.
Many plugins create short codes to display their content. Then you just put the short code somewhere on your site. If it’s defined by the plugin, you would have to read the plugin code to see what’s going on. The name of the shortcode (i.e. the first thing after the [ character) might give you a hint as to which plugin defined the shortcode.
I use and recommend a plugin called Short Code UI. That allows you to create your own short code using the WYSIWYG editor, and place that content anywhere you want. If that is installed and active, look at the Short Codes menu item in the WordPress admin navigation.
I also recommend Shortcodes Ultimate. That is a package of 40+ shortcodes that are already defined for you. This plugin’s entry in the WordPress admin navigation is labeled “Shortcodes”, which is different from the one above, labeled “Short Codes”.
You can also define a short code in a file in your template called functions.php. If you had somebody else build your site, and you’re looking for the definition, it might be there. Go to Appearance > Editor, and select “Theme Functions (functions.php)” to review the contents of that file.
If it’s in the plugin code or in functions.php, you must be able to edit PHP code to make changes. Be careful! You can lock yourself out of your admin panel if you edit a PHP file and make a simple syntax error.
That’s why I use SCUI with my customers. It enables them to create a chunk of content and reuse it in many places, without requiring PHP skills.