What i had to do is fold up your goped fold it up and hold it sideways at the pivit point of the handle bar stem their should be a little whole. in the whole their is a little back tube in it. you have to get the tube out. my dad and i used a drill bit and a mallet ( very Effective)

wonce you take that out you can take the stem cleanly off when you done use the mallet and hit it back.