You don't really need to "sharpen" those blades. If you have your manual, read what it says about sharpening the blades. All you'll want is a bevel (1/16th to 1/8th) on the cutting edges. If you have jackstands and an angle grinder, raise the cutter, put the jackstands under it (BE SAFE!!!!!!!!!!!!) and touch up the edges.
If you don't have a manual...well, Land Pride is pretty good about sending them out. Hard copies might cost you a few bucks...
If you are intent on removing the blades, make sure you torque them down good and tight when replacing ("good and tight" might mean between 300 and 500 foot pounds torque value)