I use the abba bead breaker in the link above, and good quality tyre levers once the bead has broken.. I bought the abba bead breaker as part of the full Abba kit which included the wheel balancer, tyre levers, rim protectors and some fitting gel.. Total cost was £185, sounds a lot (and is) but at £12.50 per tyre change at my local place it's already paid for itself in 3 years..
Sometimes the tyres come off easily and sometimes they can be stubborn, tyre construction plays a part here, most tyres have a hard carcas and they can be troublesome but Pirelli and Metzellers (owned by Pirelli) are softer and easier to work with.. It usually takes a couple of hours to change a tyre, including removing from and replacing back in the bike (fronts are easier here).. I'm careful and take my time.. If friends bring me loose wheels I can usually complete the change, and balance, in an hour..