as far as the stem is concerned if you have to ask perhaps you should not remove it. you need to be able to readjust the bearings, as stated, when reinstalling. if you can't figure out how to remove it, you may not have the aptitude to adjust the bearings.
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk