You can update applications installed trough Discover via the GUI in the updates menu of Discover or with apt using these commands
sudo apt-get update
sudo apt-get upgrade
the first will only update what versions are available and the second will then download and apply those updates to all your applications.
However the version available in the official repos might not be the latest version. To get this version you should look on the official websites off each app (or their github page). There you might find instructions on how to add their repo, which will then let you update from them through Discover or apt-get
For example Stacer has their own repo listed on their github page under PPA Repository (for ubuntu)