How do I tell the rate of a particles acceleration speeding up and slowing down when the function of the particle is "s" in meters, "t" in seconds, and s(t)=t⁴-6t³-4t²+4?

Other relevant info is, s'(t)=v(t)=4t³-18t²+8t and s''(t)='v(t)=a(t)=12t²-36t+8