Updating old mac operating system
Sierra will probably run significantly slower than Snow Leopard and I'd recommend at least 4GB and an SSD or at least 8GB of RAM.
Here's how Apple says you can upgrade via their mac OS upgrade page. If you’re running Snow Leopard (10.6.8) and your Mac supports mac OS Sierra, you will need to upgrade to El Capitan from the App Store first. If you’re running Leopard and would like to upgrade to mac OS Sierra, first you’ll need to upgrade to OS X Snow Leopard.
I want to update from Mac OS X 10.6.8 to the newest version which is mac OS Sierra.
My Mac should be able to run this version of mac OS.
Every time you launch a Java applet, a Java Web Start application or the Java Control Panel, the system first launches your program and then, in the background (so that performance of your Java application is not impacted), it determines if it has checked in the last 7 days for a Java update.
If you choose Skip This Version, but later decide to check for an update, you can launch the Java Control Panel by clicking the Java icon in System Preferences. If you choose Remind Me Later, you will be reminded of the update the next time you run Java.