Dear student!
Increase in temperature means an increase in molecules' speed (kinetic energy). So the molecules move faster and there will be more spontaneous spreading of the material which means that diffusion occurs quicker.
It increases the rate.
For ex: If we add 3-4 spoons of sugar in a cup of water, it will diffuse and dissolve slowly to mix but when, it is heated the sugar dissolves more faster which shows that the rate of diffusion of molecules increases with increase in temperature.
Regards