iShowU Instant has automatic updating built-in, meaning that you don't need to go and download a new version and manually install it; you can do it all from within the app.
Enabling automatic updates
To enable automatic updates, open iShowU Instant Preferences and check the Automatically check for updates box. If you would like to receive beta updates (these may be unstable and cause crashing or data loss) then tick Also check for beta updates.
Installing an update
When an update is available, a dialog will pop up telling you about the new version and what changes and fixes it includes. To install it, simply click Install Update. This will install the update and then restart the app, so make sure you're not doing anything important when this happens.