It's actually pretty simple. You need to remove the stem. Also, loosen the headset. There should be a nut on the top cap. Just loosen that until it comes out.

You have to remove the stem also and take off any spacers. Be careful not to lose any of the bearings if they are the loose kind (in the headset) and if you plan to replace the fork...make sure you remember exactly how the headset goes together. ..... I didn't do this once and put my bearing cups in upside down