You can check version of programs installed under apt with command:
dpkg -l
You can check a current package by referencing the Ubuntu Packages Search. Alternatively, for any package under apt (assuming that you have the updates repository enabled), you can use the apt-get command to update your package information and check for upgrades:
apt-get update
apt-get dist-upgrade
If you are not logged in as root (which is generally to be avoided, you may have to use sudo to have sufficient privileges):
sudo apt-get update
sudo apt-get dist-upgrade
Check the apt-get man page for more options.
Finally, you can search (or subscribe to) Ubuntu security notices to keep yourself notified real-time of needed updates.