About cleaning lenovo ideapad flex 14?

I have it since last december and recently it starts lagging alot whenever i'm playing games whenever i ask wat caused it i always get becos its overheating and i should clean it but i doubt so cos i have a cooling pad and use it in aircon room but i'm gonna giv it a try anyways. So, my question is how do i clean a ideapad flex 14? There's no access to the internal part of the laptop at the bottom i removed all the screw but still can't open it… Where could it be? And should i let a professional handle it since i don't know how to clean it and might screw it up