Change them all. Drain the fuel tank. If the bike has a carb., you will need to supply vacuum to the petcock for fuel flow. Probably needs a new battery also. No need to get expensive on the fluids until it has been run in a little. Use a good 20-50 dino for the engine, HD chaincase fluid for the primary and a good 75-90 gear oil for the transmission. Change the oil filter also. It would probably wise to bleed the brakes also. The brake fluid is Dot 5. Get some Tri-Flow and spray all the movable parts like the hand levers,kickstand, floorboard, hinges on the bags and things like that. They come pretty dry from the Factory. Check the tires carefully. The Dunlap 402's can and will get hard with age. Probably be a good idea to replace them if there is any doubt. Use some common sense and enjoy your new ride.
Just remember, HD stands for a Hundred Dollars.
Congratulations !