Firstly, you may find it easier to use webupd8's PPA. You can find more information at the launchpad page for the PPA. https://launchpad.net/~webupd8team/+archive/ubuntu/java. To add this PPA, run:
sudo rm -r /usr/lib/jvm/java-8-oracle # to remove the current installation
sudo apt-get install python-software-properties # to install the extra commands to add the apt repository
sudo add-apt-repository ppa:webupd8team/java # to add the PPA (accept the prompts)
sudo apt-get update # to get the repository info from the PPA
sudo apt-get install oracle-java8-installer # to install the oracle java (version 8, what you previously had installed)
sudo apt-get install oracle-java8-set-default # to set the newly installed java as default
In order to update, you can simply use your normal update procedure.
If you choose to continue with the downloading from Oracle method, you need to complete the following steps:
- Remove the old installation.
- Download the tarball and install it.
To remove the old installation, you can simply run in a terminal
sudo rm -r /usr/lib/jvm/java-8-oracle
And then use the same installation steps as you used previously. If you need help with this, please see this question.