How to wind back handbrake caliper piston..

[huzilulu]

Hey Guys

I am trying to install the handbrake caliper, but it won't fit because the pads are a little too tight - the rotor is 30.5mm and the clearance between the pads is 29.6mm... I need to move the pads apart a little bit more, and have been advised to wind the piston back a little bit - can someone please guide how best to do so?

Thanks