A pedal bearing is a cup-and-cone bearing just like other bearings on a bike. The problem is that you NEED a socket wrench to be able to turn the lockring precisely, because there's no way to get a normal flat wrench around the spindle. You'll need metric sockets too. Lucky for me, I work in a physics lab where we are well-stocked with nearly any kind of tool (including machine tools ).

For the Nashbar pedals, remove the dustcap (and the cage if it's the platform/clipless combo pedal). Then look at the spindle: you'll see a lockring that takes a 14 mm socket wrench I believe (be sure to check that). Hold the axle of the pedal with a pedal wrench or adjustable wrench, and loosen the lockring with your socket wrench. Once you've got the lockring loose, there will be a washer, and then finally the adjustable race and the bearings. If you know how a cup-and-cone bearing works, this should be all you need to know in order to adjust the pedal bearings.