What happens to acceleration when Fnet increases and mass stays the same

acceleration propotionally increases to force

Explanation:

According to Newton's second law of motion

The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

in another form,

Force = mass * acceleration

when mass is a constant

Force ∝ acceleration