I have a couple of options. We use large pedestal belt grinders at the shop and that's generally what I use. At home depending on how dull they are I use a file while the blade is clamped in a vise.
Either way I always check the balance and work to get them as close as I can. I think that and using synthetic grease in the spindle bearings really goes a long way to increase bearing life. My Cub Cadet 2518 has 540 hours on it and still has the original bearings in the spindles.