There are many ways to check Java version. My favorite is: type "java -version" in a shell.
In Windows to open a shell press "Start->Run", write "cmd" and click on "OK".
To close a shell write "exit" in the shell and press enter.

Example of output:
java version "1.6.0_01"
Java(TM) SE Runtime Environment (build 1.6.0_01-b06)
Java HotSpot(TM) Client VM (build 1.6.0_01-b06, mixed mode, sharing)

Note: in many places 1.6.0_07 will be referred as Java Version 6 Update 7. These are equivalent ways of stating the same (version).