As someone who's sat re-sits for GCSE History and Maths-Numeracy (Welsh qualification) I can tell you they're different papers. I wouldn't say they're slightly harder papers in terms of difficulty...they're about the same difficulty as the original you sat. I'd recommend thorough revision (I'm not assuming you didn't revise the first time, I'm just telling you to revise again). It may seem pointless if you already revised for your original exam/s but it'll be worth it when you get your results. I, for example, was entered in Year 10 for my Unit 2 History module, in which I had a D. After re-sitting this paper in Year 11 with the other two modules, I had an A in my re-sit paper. I also had a D in the November entry for Maths-Numeracy so I re-sat in exam season and had a C.