Our repair agents or a bike shop should be able to help you. To do it yourself, here are the instructions:
To remove the axle:
Remove the hubcap. Push nib spring down and towards the open end of the axle so it is flush. Remove the starlock washer (the teeth need to be bent to remove it). Once the starlock has been removed place the wheel axle downwards against a hard surface and excert downwards force so that the axle slides through the bearings. Bearings can then be removed.
To replace the axle:
Do as above and below are the instructions on how to add the washer:
Put the washer at the top of axle pin, so the lip of the washer is facing upward. Take a hammer and tap each side of washer alternately downward with the hammer to start the washer moving downwards to the wheel.If you can, locate something hollow that will fit over the axle pin and the lip of the washer (a hollow ended broom or ratchet socket), tap this with a hammer to push the washer down to the wheel until it is snug.