you have to remove the wheel and brakes and fender. Then loosen the bolts that clamp that fork into the upper and lower triple clamps, then slide that fork down and out of the triple clamps.
Get a manual and read it, owning an old motorcycle demands that one become motorcycle literate at times. Besides knowing what the parts are called, you'll know what the heck we're all babbling on about here in these forums.
Many different types of old motorcycles have a way of turning ordinary people into mechanics.
Welcome!