Fork seized to frame: can I just hammer it down now?
To remove the fork the tapered spacer on the top need to be loosened. Tap the top of the fork (maybe a little harder than you have). Then push the fork back up into the seated position. This should allow some clearance between the tapered collar and the headset bearing. Removing the split tapered collar should make everything loose enough to disassemble. Lay all the pieces out as you remove them and take a photo. It can be confusing putting it back together as the parts only fit together one way. If the bearings are open caged type you can clean and regrease them. If they are sealed then they will need to be replaced.