Honda mower question

Hi I decided to service my mower myself this year, oil is easy to change but having a heck of time gettin the blade off to sharpen. Cant find my manual. Is there a trick to getting the blade off. I've got a Honda Harmony HRT, about 8 years old. Original blade. I was wondering if maybe after 8 years I should get buy a new blade? Its one of those mulching blades. Also, when it runs it seems to rev up and down after a few minutes, does anyone know whats causing this?
any help greatly appreciated
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The trick is to not leave it on for 8 years. In general, it helps to have some kind of wedge (wooden) to keep the blade from spinning and an impact tool to loosen nuts & bolts. (either a pneumatic impact wrench or one of those $10 socket drivers you wack with a hammer or a breaker bar and hammer).
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off.
Check your belts- it sounds like one is slipping.
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