Where my picture says "Download" you will see a price to buy Mountain Lion. Click on that button and enter your AppleID password to purchase Mountain Lion. It will then download into your Applications folder. It is about 4GB, so it may take some time.
Given that you are self-admittedly "techno-challenged," do you know that some of your programs will not work with Mountain Lion, even though they work just fine with Snow Leopard?
You can research all of your software here: http://roaringapps.com/apps:table