mark around the existing slam panel with a scriber or centre punch by the edges so you can see the panel alignment
grind though the spot welds with angle grinder on the welds on the bracket below the headlights
and at the top of the inner wings, as the metal gets thin, you can prize the slam panel off with a screwdriver
its not that hard to do, if you take your time and mark the position for the new slam panel first..
... I also tempararily put the wings back on the car to check the alignment too, but this isnt shown in the photo.
then remove the old slam panel
then clean up any old paint or rust off the edges of the inner wing (the punched marks makes it easier to line the panels up later)
check the alignment of the panels for fit.... I found that one of the straps under the light was in the wrong place so needed replacing and a hole that the wing bolts through needed filing as it was in the wrong place
when you're happy with that you need to drill some holes (5 or 6mm diameter on the slam panel where its welds to the inner wing. this allows you to plug weld it (equivalent to spot welding) and prevent distortion, and clamp it in place before welding it.
you also need to drill 2 or 3 holes where the bottom of the slam panel sits on the headlight bowl of the and the bracket at the end of the chassis rails meets the slam panel, but the holes may be very close to the edge
thanks to Dom - optima21 for writing this guide