You don't have to change any php code line. Just put some additional css rules within your theme (which one do you use?) and target that particular question in particular quiz, so the other questions would not be affected by them. You can do it by obtaining id tag from the source code of the page.
There are plenty of css solutions and variations for this, if you are capable to do these two steps from above, we can help you with more information.
For example, here I have all four images in one row, but it be can broken too into the two rows. Also, the images could be responsive or not, etc.
You can see that I hid radio buttons and showed just images that were clickable all over their area.
The first solution seems OK if it is just one question so you don't want to put much effort in it.
I would prefer this one for uniform tests with a lot of questions.