Easy as pie to do pal. Drill your existing threads out to 5mm. Buy your self a set of M6 taps (a set contains 3 taps) and a tap wrench Tap away!!! lol The taps go through an order, if you look at the top of the tap, there's a recessed area. the larger the area, the sooner you use it, if you understand me, lol. Insert the first tap into the hole, with the tap in the wrench, apply light downward pressure and turn 1 full rotation in a clockwise direction, then back half a rotation anticlockwise. Continue until the whole of the hole has been tapped, repeat with 2nd and 3rd tap. if your tap starts to get really stiff when your turning it through the full clockwise rotation, ease off, as you may snap the tap, and they are a pain in the arse to remove . Just remember to keep your tap level whilst your doing it, or you'll end up with bolts on the piss . Cheers, Josh.