To clean it first start with a cool engine. If your mower has a fuel valve switch it off. If you can disconnect the spark plug too. Next use a leaf blower to blast away any old dirt and major debris. Now gently lay the mower on its side fuel cap facing up. Try to get rid of any junk on the mowers underside as well.
For the past three years we have used the Greenworks 22502 Corded Lawn Mower on our ¼-acre lawn. We particularly like how easy it is to adjust the blade height and it is surprisingly light. There are just a couple negatives we have noticed. We live in the Pacific Northwest where mowing wet grass is unavoidable. When the grass is wet it does not feed into the bag of this mower easily. Also we had to replace the cord after my teenager ran over it with the mower. So cord control is important and takes a little planning.
After sharpening both sides of the blade place it on the kits cone-shaped balancer. If one side dips below the other continue sharpening it until the blade rests level. Return the sharpened blades to the mower and reattach. If you have a torque wrench its a good idea to use it here. Often you need to tighten the blade mounting bolt/bolts to a specific tightness level. Typically measured in pound-feet your instruction manual should list these specs. For example my personal machine the Honda HRR216VKA between 36 to 43 lb-ft of torque is required.