There are three "normal" ways to quit a program: hit Cmd-Q while in the program, go to the ezCheckPrinting menu and pick "Quit", or right-click the app's icon in the dock and pick Quit (or sometimes Force Quit will show up here if the app is stuck).
If those methods don't work, you can force-quit the app by hitting Cmd-Option-Esc to bring up the force quit window.