When I try and update
sudo apt-get update
I have natty 11.04
W: GPG error: http://packages.medibuntu.org natty InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 2EBC26B60C5A2783
W: Failed to fetch http://archive.getdeb.net/ubuntu/dists/natty-getdeb/Release Unable to find expected entry 'game/binary-i386/Packages' in Release file (Wrong sources.list entry or malformed file)
E: Some index files failed to download. They have been ignored, or old ones used instead.
and a laptop with 4GB ram and i5 processor
What should I do?