Changing Java to new jre

Type which java to get the current location of the link, remove the link with rm then recreate the link pointing to the new version.

$ which java/usr/bin/java

$ ls -ld /usr/bin/java

$ rm /usr/bin/java

$ ln -s /usr/bin/j2re1.4.2_17/bin/java /usr/bin/java 

$ ls -ld /usr/bin/java

NOTE: usually in ubuntu, the defaul jdk location for openjdk is
/usr/lib/jvm/java-6-openjdk-armhf/jre/bin/java


original post appeared here, all credits goes to him:
http://www.unix.com/solaris/66893-setting-link-newly-installed-java-version.html