What is the OS you are running your JSS on?
Usually just go to JAMFNation, log in and go to your "Assets" and download the latest version for the correct OS. Since it is downloaded, there is a full description attached on how to update for each OS.
Think the most important thing for every Update/Upgrade - backup your most important data before. For a JSS, I definetly recommend to back your Database before. If you are running your JSS on a VMServer, I would recommend to "Snapshot" the VM as well.
Location JSS Database Utility
Hard Disk -> Library -> JSS -> Bin -> JSSDatabaseUtil.jar
Location Casper Suite 9.3
1) Log in your ID JAMF Nation
2) Click at your ID name, it show menu - My Assets, My Support, My Profile, My Bookmarks, click on My Assets
3) My Product show latest version of Casper Suite