sudo update-alternatives --config java
An output like this will show up:
There are 6 alternatives which provide `java'.
Selection Alternative
-----------------------------------------------
1 /usr/bin/gij-4.3
2 /usr/lib/jvm/java-gcj/jre/bin/java
3 /usr/lib/jvm/java-6-sun/jre/bin/java
* 4 /usr/lib/jvm/java-1.5.0-sun/jre/bin/java
+ 5 /usr/lib/jvm/java-6-openjdk/jre/bin/java
6 /usr/bin/gij-4.2
Press enter to keep the default[*], or type selection number:
All to do here is enter the number of the selection next to the alternative JRE name and press enter.
Hope this was helpful. Enjoy.