Hello there and welcome to the forum gosh it's getting busy on here now guys
I'm not sure of the size allen key, all my workshop manual says is remove the bolt (so possibly a socket rather than allen key) although this is something I'll be tackling next month (putting a set of highly controvercial (on here anyway) EBC GreenStuff uprated pads on so maybe you can help me!
I have the removal and re-fit procedure though if that helps
found out it's 7mm same as the fords! take the wheel off then 2 caps loosen bolts remove spring and pads then push pistons back, copper slip pads then refit easy gotta do it tomorrow on mine and a mates mondy