You will have a Java preferences folder in the Utilities folder if installed. You would also know because eventually you would come across a website telling you that you need to install Java in order to view it.
For the update, run software update. If you need it, it will be there to update. If it shows, install the update.
Under Safari Preferences, select the Security Tab. You can disable it by unchecking the box for Java.
Or, open Java Preferences in the Utility folder and under the General tab, deselect the Enable Applet Plug-in.
The Java update from Apple will disable this automatically if not used for a period of time.