error : E: Some index files failed to download. They have been ignored, or old ones used instead.

sudo rm /var/lib/apt/lists/* -vf 
sudo apt-get clean 
sudo apt-get autoremove 
sudo apt-get update 
sudo apt-get dist-upgrade 

Now I was facing a GPG error. To solve this I tried the following

$ sudo -i # apt-get clean # cd /var/lib/apt # mv lists lists.old # mkdir -p lists/partial # apt-get clean # apt-get update # exit 

After this command. I entered the final commands.

sudo apt-get dist-upgrade