These days you can also pin the currently-installed version with:

apt-mark hold yourpackage

and unpin it with:

apt-mark unhold yourpackage

You can see all held-back packages with: apt-mark showhold

sudo dpkg -P $(dpkg -l | awk '/^rc/ { print($2) }')

You just need to do apt-get install --only-upgrade <packagename>. This will upgrade only that single package, and only if it is installed.

If you wish to install the package if it doesn't exist, or upgrade it if it does, you may leave out --only-upgrade.