How to fix case heat buildup in Deepcool AK500 for stable gameplay?

Long dialogues made my AK500 case hot, causing frame stutters. I opened the side panel, but it was dusty and noisy. I used GamePP to raise the front fan to 1000 RPM and rear to 1200 RPM. GamePP Hardware Sensor Page showed CPU temp at 72C and frame time at 8-10ms.