404 Error updating from 10.10 to 11.04

I am trying to upgrade from 10.10 to 11.04, so that I can then upgrade to the newest version. I don't want to to just download the new ISO file, because I finally got the computer set up the way I want it, and then realised it was out of date. So I want to just upgrade through the Update Manager. But when I try to do that, I get this message:

W:Failed to fetch http://extras.ubuntu.com/ubuntu/dists/maverick/main/source/Sources.gz 404 Not Found
, W:Failed to fetch http://extras.ubuntu.com/ubuntu/dists/maverick/main/binary-i386/Packages.gz 404 Not Found
, E:Some index files failed to download, they have been ignored, or old ones used instead.

Trying to go to those sites on my browser also results in a 404. I know this is probably because those are old, and they moved the pages. But, it seems like they are still supported, because Ubuntu's page on upgrading still has "Natty Upgrades" in a distinct different section than its "obsolete" section. It tells me to:

Network Upgrade for Ubuntu Desktops (Recommended)

You can easily upgrade over the network with the following procedure.

    Open the Update Manager application from the System → Administration menu.

    In Update Manager, click the Settings... button, and enter your password to start the Software Sources application.

    Select the sub menu Updates from the Software Sources application.

    Check the "Release upgrade - Show new distribution releases" drop down to make sure "Normal releases" is selected, and change it if otherwise.
    Close the Software Sources application and return to Update Manager.

    In Update Manager, click the Check button to check for new updates.

    If there are any updates to install, use the Install Updates button to install them, and press Check again after that is complete.
    A message will appear informing you of the availability of the new release.

    Click Upgrade.
    Follow the on-screen instructions.

It says that as if the link should still work. It doesn't. So I need someone to tell me how to change the destination site for the upgrade manager, and/or how to upgrade some other way that won't result in a reformat. I am new to Ubuntu, so I need it told to me in as non-nerdy a way as possible