You need a 'parallel punch', I can't remember offhand what size as I have got a set of all different sizes, it's just a handle with a very accurately made cylindrical bar of a particular size sticking out, you have to gently tap out the pins that hold the guard into the body of the pistol by placing the punch on one end and gently tapping with a small hammer to drive the pins out. Be careful though, you need to look carefully at the body of the pistol and decide which side they were tapped in from in the first place then tap them back out that way to avoid widening the holes, also, the trigger guard holds in a spring at the front of the guard, take the old guard off carefully and it should stay in place.