Download and unpack java at /opt/java/, this way you can keep all past versions in one place configuring only update-alternatives.
Following examples use version jre1.7.0_60. Java binaries or libnpjp2.so location may differ.
Basically is install and configure:
~$ sudo update-alternatives --install "/usr/bin/java" "java" "/opt/java/jre1.7.0_60/bin/java" 1
~$ sudo update-alternatives --config java
This trailing number in the end is some kind of priority, I always set it to 1. In following config screen that show all installed versions, you need to select the newest version and press enter.
~$ sudo update-alternatives --install "/usr/lib/mozilla/plugins/mozilla-javaplugin.so" mozilla-javaplugin.so "/opt/java/jre1.7.0_60/lib/amd64/libnpjp2.so" 1
~$ sudo update-alternatives --config mozilla-javaplugin.so
In the same way the following config screen will show all installed versions, select the newest version and press enter.