I wanted to put a new set of blades on my Honda Harmony mower. I am having a difficult time removing the old blades. Any suggestions?

You need to remove the plug wire to prevent starting.

Then get yourself a 6 point socket. 12 point sockets and adjustiable wrenches wrenches are not a good idea.

Use a breaker bar. A large bor with a 3/8 square drive.

You'll have to wedge a block of wood between the blade and the mower deck.

If things get really tough, you can use a strap wrench on the shaft. This won't mar the shaft.

After you do it the first time, then every other time will be very easy because you will put anti-seize compound on the threads.

Kiss has given good advice.

Yep, comes from working on cars. That harmonic balancer bolt torqued to 150 ft-lbs is a real tough one to remove by hand. In that case it's a 1/2" breaker bar with an impact socket. Normal Craftsman sockets will break. Normal MAC Tools sockets won't. Impact sockets are a better bet. Always used Anti-Seize and a torque wrench.