Changing the temperature would cause an enzyme's activity to
increase or decrease. As enzymes are protein molecule,high
temperature would cause denaturation of the protein resulting in
decrease in enzyme activity. So changing
the temperature is correct
option.
Increase in substrate concentration initially increases the rate
of reaction i.e the reaction velocity would increase until it
reaches a maximum velocity after that point, increase in substrate
concentration will not increase the velocity. Enzyme activity never
decreases by increasing the substrate concentration.