sudo apt-get update
Only updates the repository , use
sudo apt-get upgrade
Upgrade is used to install the newest versions of all packages currently installed on the system from the sources enumerated in /etc/apt/sources.list.
sudo apt-get dist-upgrade
Dist-upgrade in addition to performing the function of also intelligently handles anging dependencies with new versions of packages; apt-get has a "smart" conflict resolution system, and it will attempt to upgrade the most important packages at the expense of less important ones if necessary. So, dist-Upgrade command may remove some packages.
As mentioned before update will install all the newest packages , If you only want to update a particular package use-
sudo apt-get install package_name
But if everything other then that package is already updated , you can directly use UPDATE.