There are several types of securing bolts for the propeller nut.
1) Bolt with allen hex key (secured with loctite or similar)
2) Bolt with hex head, secured with fold-in teeth-washer (like on picture from fenders). This bolt has a tread-lock agent too, if fitted new.
In both cases, you have to undo the securing bolt first, which is RH tread, so undo anticlockwise. As Tommi mentioned, heat would possibly help.
If you have undone the securing bolt, you can undo the propeller nut (this is the whole cone!), with has a RH tread, so undo anticlockwise too.
If the head of the securing bolt is damaged, and can't be undone, you can:
a) Try to work a slot into the damaged head and undo with a slot-type screwdriver
b) drill out the head. But this means you have to remove the remnants of the bolt out of the propeller shaft with a mole grip (again heat will help!!).
If the remaining lenght of the bolt is to short to catch with the mole grip, you have to remove the whole propeller shaft and drill out out the remnants. But this is usually a workshop-job.
If nothing of above: new propeller shaft