I have a server that I've forgotten to upgrade for ages, which is still running Intrepid (8.10). I'd like to upgrade it to a newer version of the distribution, so that I can get security patches etc. I found some instructions that tell me to install the package update-manager-core. I tried the following:

$ sudo apt-get install update-manager-core

but this fails since some of the necessary packages can't be found:

...
Err http://archive.ubuntu.com intrepid/main python-apt 0.7.7.1ubuntu4  404 Not Found [IP: 91.189.88.40 80]
Err http://archive.ubuntu.com intrepid-updates/main update-manager-core 1:0.93.34  404 Not Found [IP: 91.189.88.40 80]
Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/p/python-apt/python-apt_0.7.7.1ubuntu4_amd64.deb  404 Not Found [IP: 91.189.88.40 80]
Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/u/update-manager/update-manager-core_0.93.34_amd64.deb  404 Not Found [IP: 91.189.88.40 80]
...

I know that Intrepid is no longer supported, and so I guess some of the necessary files may no longer be maintained. But this seems rather unhelpful: I can't upgrade because it's too old, and the only way to fix this would be to upgrade it. Is there a way round this? Is something else wrong?