Slight upgrade for my PC

Hello guys so here is my PC at the moment:
Case - CoolerMaster K350 Black
MB - Asus F2A55
Power Supply - Corsair 750 watt modular 80 plus
CPU+cooler - AMD A8 5600K Quad Core 3.6Ghz ( never overclocked ) With CoolerMaster Hyper TX3 Evo heatsink and Fan
Memory RAM -2x4 GB Samsung 1600MHz
Video Card - Sapphire R7 260X 1GB DDR5
Primary SSD - Samsung 850 EVO 120gb
Secondary HDD - WD 1TB

So, I am looking to sell my MB with the CPU and replace them with something a bit better but not top notch. The first stupid question is INTEL or AMD? And What MB would fit in my PC case?
I am even considering upgrading the CPU only but I don't think I have many options with my current motherboard...Any ideas ?
 
Well to be honest I have just bought this video card 2 weeks ago, I had a GTX650 1GB and I can honestly say that the R7260X is much better than the GTX 650. I am a real noob so if you can explain what running on 1080p means I would appreciate it. 1080p for me is better quality on youtube and that's about it haha