Starting from the well-known quantum Miura transformation for the Lie algebra An, we compute explicitly the OPEs for n = 3 and 4. The primary fields with spin 3, 4 and 5 are found (for general n). By using these primary fields and the OPEs from quantum Miura transformation, we derive the complete structure of the nonlinear W4 and W5 algebras. It is known that the quantum Miura transformation fo...