how can i ajust the verical hold on my tv, goodmans gtv 51dvd?

We have a goodmans dvd tv, for some reason there is a part of the picture to the left hand side that is missing, ie, you may not be able to see the full credits or program info, it's not the end of the world but it is annoying, the set is about 7 years old, I think years ago there would have been a couple of knobs on the back to ajust the vertical and horizontal holds, not any more though, Any help would be grateful,
Cheers Pete.