Hi Angela,
Four by three or four to three is the aspect ratio: four parts the longer, horizontal side of the image, three parts the shorter, vertical side. You probably have 16:9 aspect ratio video if your TV station doesn't like it that way; it's a wider picture.
I see two principal options for you:
(1) Sacrifice the sides of your video to make the middle part of the 16:9 picture fill the entire 4:3 screen or
(2) Have the 16:9 picture fill only part of the 4:3 screen with empty/black stripes at the top and bottom, which is the traditional way of showing wide screen flicks on TV.
In either case, you need to click on the aspect ratio button at the very top menu in the Edit module, to the left of the cogwheel icon, to switch from 16:9 to 4:3.
For option (2) above, you're done.
For option (1) above, use the Modify button to open the PiP Designer windows and draw the top and the bottom of the picture to the edge of screen.
I think you need to produce/render the video at 720×576 pixels although this is not really 4:3. I am not exactly sure about the most convenient output format. If I were you, I would try samples in different formats for the TV to choose from if possible.
Good luck…
Jirka