I'm renovating an old mountain bike. I'm not up on some of the tech, having learnt my bike mechanics back in the 70s.

The headset is grinding so I want to disassemble and replace the bearings.
See photo.
There is no bolt in the gooseneck -- I assume this is correct? I guess there should be a plug or stopper, but it isn't required mechanically?

How is the headset locked to the fork then?

To disassemble do I just loosen the big locknut?

This may seem obvious, but I've destroyed hardware before by trying to force it to do something it wasn't designed to do.