Ctrl+c cancels it but next time start from where you left
Ctrl+z stops process but then you can't do another process as it remains locked to the first process

Using one of the above methods is generally better than just closing the terminal, but if you just close the terminal while it's downloading packages, it should start the download right where it stopped next time you run sudo apt-get upgrade

If you want to restart the download after using Ctrl+z:

1. Check paused tasks by typing jobs in the terminal


2. To resume a process, type fg


3. If you have multiple tasks, then type fg 1, fg 2, etc…

Make sure, however, that you never stop it while it's installing the downloaded packages, since this will result in a lock on apt-get, which will require a computer restart or reconfiguration of apt, and you'll have to start at the beginning of the installation.
So make sure to only "pause" (close) the terminal when it's downloading, not installing.

If you would like to start another apt-get process - after pausing the first process, run sudo rm /var/lib/dpkg/lock && sudo rm /var/cache/apt/archives/lock; it won't look like it did anything, but you should be able to start another apt-get process.

To kill a command that you've paused with Ctrl+z, enter kill -9 %x into the terminal, replacing x with the number that the paused process is (see jobs). The process will remain in the list, but it will say "killed" after it instead of "stopped", indicating it is no longer active.

Sources : [ubuntu] How to pause download operation in terminal

Accidently pressed Ctrl-Z in a Linux terminal in Ubuntu Intrepid Ipex. What do I do now?
Starting, Stopping and Managing Jobs in the Ubuntu Terminal