Changing a tyre with disk brakes

Hello all i have a Carrera Subway 8 bike, which has quick release wheels and disk brakes, they are Nexus Inter 8 Componenet package all the gears and brakes are covered up.

My problem is that i don't know how to take the wheels off front and back, i use the quik release lever, fine, then i try to pull out the wheel but the brake cable is still attached to the bike, how do i get this off it's driving me nuts!

Help!
Richard