First, remove the 2 Phillips head screws that secure the dust cap to the wheel center. You may need to tap the dust cap with a screwdriver handle to break it loose.
Next, remove the upper collar. Using the 1/8" hex wrench, loosen the upper collar set screw. You may need to wet the collar and shaft with vegetable oil if the collar is not easily rotated or removed. After several applications of vegetable oil, use pliers to rotate the collar. Upward pressure with rotation should remove the collar.
Next, remove the wheel from the wheel shaft or axle. If corrosion is present, you may wish to put a few drops of vegetable oil on the shaft and bearing to help loosen.
The bearings are a flanged, press-fit bearing. To remove the bearings, insert a screwdriver through the hole in the bearing. Gently tilt the screwdriver. Use a circular tilting motion to gradually lift the collar edge (flange).
Next insert the edge of a flat blade screwdriver under the flange, twist the screwdriver slightly so the bearing begins to elevate. Repeat this in several positions around the bearing so the bearing moves up evenly. If this is done gently, no damage should occur to the wheel.
Continue elevating the bearing until it comes free of the bearing hole. If high, uneven force is used, you may bend the bearing seat.
Picture at right shows bearing hole after bearing has been removed.
Repeat this process with upper bearing in the center of the wheel.
Picture at right shows flat blade of screwdriver being used to elevate upper bearing flange.
To install the new bearings, place a bearing on the bearing hole and firmly press it in with your thumb. You may need to rock it back and forth.

Next, clean off shaft and the collars using vegetable oil. The oil will soften any deposits. Wipe clean with a paper towel. Loosen the set screw in the lower collar, place the lower collar on the axle (shaft) and be sure it easily rotates on the shaft. Slide the wheel onto the axle (shaft). Then position the upper collar on the end of the shaft so the shaft does not extend beyond the edge of the collar. Tighten the set screw to lock the upper collar in this position. Next, press the lower collar up toward the upper collar so the wheel is pressing against the upper collar. Tighten the lower collar set screw in this position. Once both collars are correctly installed and tightened, apply some white glue (Elmers or Tacky) to the underside of the dust cap and screw the dust cap to place. For pictures and a more detailed description of wheel re-assembly, go to the Assembly and Installation Page

Link to Assembly and Installation Page