Enzymes increase reaction rates by
MECHANISM OF ENZYME ACTION
Explained by different theories:

Lowering of activation energy
Michaelis-Menten theory
Fischer’s Template theory
Koshland’s Induced Fit theory.

Lowering of Activation Energy
Enzymes lower the activation energy. Activation energy is defined as the energy required to convert all molecules of a reacting substance from ground state to transition state.
Altering the free energy of the action
Inhibiting the backward reaction
Enhancing the forward reaction
Decreasing the energy of activation