What’s the difference between M7 and M8 for GCSE Maths?

My teacher has entered my class in for the M4 and M8 but originally we were meant to be in M7, she says difference is that with M8 it’s possible for me to get an A* instead of just an A. I’m not very good at Maths, and I’m aiming just to pass, maybe even a B. What’s the difference between both tests? If M7 is easier I’d rather go for that as its more or less impossible for me to get an A* in Maths.

Im in Northern Ireland so I’m following the CCEA Guidelines, not Ofqual or AQA or any other ones.