I never had one quite that old but on a little later models...you'll have 4 blades held in drum with wedges that are bolted down. There will be three holes in each wedge. Two are for the bolts and one is empty (except for the saw dust that it is undoubtedly packed with). Clean out the empty hole, remove the two bolts and start turning one of them into the empty hole. That hole doesn't go through into the drum. Instead, that bolt will force the wedge away from the drum.
I don't remember if those blades have grooves to set them but when you replace them, you obviously have to have them all set the same. Even being off a little bit can make a big difference. You want to make sure your cutter bar has a nice, even corner on it and that the blades just barely clear it without touching it. I hope this helps. Feel free to ask me any other questions you have about those chippers.
Edit to say....I'd just take the blades somewhere that has the proper equipment to sharpen them. You can probably try it but I don't think it would be very easy to get them all exactly the same.
