If you are using Chrome right now...
Type in chrome://plugins to your address/search bar.
Find Java in the list.
OR you can...
1. Open up Chrome and go to your Settings / Preferences
2. At the bottom of Settings, click "Show advanced settings..."
3. Under Privacy, click the "Content settings..." button
4. Scroll down to Plugins, click "Disable individual plug-ins..."
5. Find "Java" on the list of plugins. Click "Disable".
In step 3, when you scroll down to Plug-ins, I also recommend choosing the option "Click to play" which requires that you click on something before any plugin can be used as an extra step of safety.