This is a 1/2" drive breaker bar: 1/2" Breaker Bar
It accepts a 1/2" drive socket at the end of it.
This is just for reference, it is a 1/4" drive 6 point socket. 1/4" Drive 6 Point Deep Socket - 1/2"
Note that there are 6 sides to the socket. Sockets come in 12 sides too. They also fit hex heads. 12 points are for maneuverability.
Typical drive systems are 1/4", 3/8" and 1/2" and you can adapt to lower drive systems.
Depending on what you have to work with and the room available 3/8" drive may be adequate. The larger the arm, the easier it is to apply the same force.
Extensions can be applied to the socket too. If you need a short reach a deep socket can be used. It will be more stable than an extension.
Hopefully, that solves one problem.
What can help to loosen rusted screws is a product known as WD-40. It comes in an aerosol can and liquid form. Spray on and wait. WD-40 - Wikipedia, the free encyclopedia
Anti-Seize compound ANTI-SEIZE COMPOUND SHEET
There are lots of varieties, but you'll usually find a small tube of it an an auto-parts store.
It's made of either Moly, Copper or Nickel, It doesn't like to come off stuff easily so I apply it with a vinyl glove. I just bought 400 gloves.
OK, those out of the way.
The bolt is is the center of the blade, but you figured that out. There are many ways to grip the bold, but most will round the head leading to very difficult problems, so I am suggesting a 6 point socket. A breaker bar gives you some manuverability downward. The longer the bar the more force you can apply. It easily breaks nuts torqued at 200 ft-lbs. That's 200 lbs at a distance of 1 foot. Provided you could exert this amount of force at 1", you could exert 400 lbs at 2' and 800 lbs at 4'. So it's a strong mechanical advantage.
Pro's may use impact wrenches.
You have to prevent the blade from turning.
You do that by holding the blade with a leather glove, but blades are sharp and the bolt is tight, so lets abandon that one until you get it off and apply anti-sieze.
The bolt comes out counter-clockwise for a typical right hand thread.
You need to create a "wedge" with a block of wood so that when you turn the bolt counter-clockwise the blade won't move. I can't make any suggestions as to where that block of wood should go.
There are other ways, but this will do no damage.