Now the air can move freely out of the tyre, it's time to break the bead. This means unseating the tyre from the rim. You do this by applying downwards pressure on the sidewall of the tyre as close to the rim as you can. Put both knees on the tyre and use your thumbs to push down as hard as you can.

If things get tough this is a quick way to break the bead http://www.webbikeworld.com/t2/bead-breaker/motorcycle-tire-bead-breaker.htm