Possible Duplicate:
How to install software or upgrade from old unsupported release?
These update errors are preventing upgrade Ubuntu 11.04. (I want to ultimately upgrade to 12.04):
http://extras.ubuntu.com/ubuntu/dists/natty/main/source/Sources 404 Not Found
http://extras/ubuntu.com/ubuntu/dists/natty/main/binary-amd64/Packages 404 Not Found
http://extras/ubuntu.com/ubuntu/dists/natty/main/binary-i386/Packages 404 Not Found
I check for updates pretty often but recently these have cropped up. I'm learning as I go but need some assistance to resolve this. Any guidance would be greatly appreciated.