I tune up and sharpen the blades on my mowers ever spring and as needed.
A sharp blade cuts your lawn better and does much less damage to the grass.
If you have never pulled a deck on a riding mower it is easy. Look for the pins pull them. Disconnect the blade engage cable. Take the belt off of the motor pulley and slide the mower deck out from under the mower.
IMPORTANT NOTE! Check how every thing is put together as you pull it off or you may add work to the job. Pull the blades with an impact wrench and sharpen them with a grinder; check for balance and reinstall.
On a push mower just tip it upside down and use an impact wrench to take off the blades. Sharpen them with a grinder and put them back on.
When you grind your blades do it from the slanted side and only take off the burrs on the flat side of the blades.
It is a very good idea to wear safety glasses or some eye protection.