Make sure ALL package installation applications (Synaptic, Ubuntu Software centre, and Update Manager) are closed.
Now try the WebUpdate instructions again.
You can only use 1 installer at a time .. and apt-get is one of them
Be sure to DISABLE the JAVA plugin in your browser .. only enable it when it's totally NECESSARY .. Oracle/Sun JAVA has MAJOR
security issues, OpenJDK/Icedtea (AFAIK) doesn't.