I changed the tires on my Z400 by myself. It's actually pretty easy.
To break the bead I just ran up on the tire with a car. The trick is to just barely drive onto the lip of the rim so as soon as any significant weight gets on it the car tire will slip off the lip and break the bead easy. You might have to back up and rotate the tire and run it over again to get the bead completley off. Then do the same thing on the other side.
Once you got that done, spray the tire and wheel lip down with some lubricant (I prefer silicone spray). I used 3 motorcycle tire irons about 6-8" long. It takes a bit of muscle, but I'm 17 and 130lbs and I could do it myself. It took me mabye 2 hours to get all the tires off the old rims and onto the new ones.
If it's nice weather out, letting the tires sit in the sun all day will make it alot easier to mount them. Just try it yourself, if it's not worth you're time or it ain't workin out then take it to a place. Ya got nothin to lose but some time.