Having jdk 8 and jdk 6 installed on Windows how to choose the default version to use (jdk 6)?

Question

for my job I need to use the jdk 6 but I started installing the jdk 8 because I prefer to use Netbeans 8 that requires it. After that I installed also the jdk 6 and I'm able to manage the two java platforms from my ide (I can configure Netbeans to use the jdk 6 when it compiles my company projects). The problem is that I'm unable to configure the java default version used by my os (I use windows 7 64). In particular from the command prompt, if I type java -version it tells me that I'm using Java 8. I want to use the version 6 in general and to use jdk 8 just for Netbeans. I started trying to modify the JAVA_HOME system property but it was not setted at all (neither with the path of jdk 8 ?!?!? ) so I create a new JAVA_HOME with the path of JDK 6 but it seems that the jdk 8 mechanism has the priority because the prompt version displayed is still java 8! Anyone could help me to switch to version 6 please?