Asumming they are 14x6 in rims, I think you can do 225/70-14 or 235/60-14 if I remeber correctly.
Best to call a tire shop. They have a book and if you tell them the size rime they can tell you what can be safeyl mounted without any tire distortion of the tread. Too wide a tire on a narrow rim will make the center of the tread bulge causing an uneven wear pattern in the middle of the tire contact patch.