Thanks Leejosepho for the quick response.
I’ve already done what you suggested, but I don’t clearly understand is if I should either create a brand new, perhaps, single.php file and copy the code from 2012’s one then edit it, or edit directly the 2012’s one.
If I choose the first option, will the 2012’s updates affect my theme? I guess they won’t, but an explanation on this matter would be really appreciated.
Thanks again.