If that '760GMA-P34 (Fx)' is the model of your current motherboard, it is an mATX motherboard. That doesn't mean you don't have an ATX case though.
The best way to know is count the number of slots. The slots are the rectangular openings that add-in cards will protrude through and line up (roughly) to sockets on the motherboard itself. Unused ones will probably have a blanking plate covering them. If there are 4 slots (which includes the slot/s the GPU is sitting in if you have one) it's an mATX case. If more than 4...say 6 or more... it's at least an ATX case.
If you have any doubts post a picture of your system if you can..back panel and/or motherboard with case cover removed.
Well, I’m considering the one that has less slots, the recommended one, I’m wondering if it affects the motherboard at all