Peter
They should clean up under normal to heavy braking however as mentioned you may need to give them a bit of stick. The correct way of course is to remove the road wheels and use a wire brush or course Emery cloth on a block and give the discs a good cleanup
If you’re feeling safe to do it remove the pads and again clean the face of the brake pads before refitting (a good time to add a bit of copper slip to the back of the metal to keep everything nice and squeal free)
They can be recovered if things have gone way too far you can get them resurfaced by Melvin Rutter who has a disc cutter but that would mean they were extremely pitted or warped in order to do this and should not really be necessary.
To answer your question about changing the discs it’s not technically complicated but a bit fiddly as you need to undo the stub axle castellated nut which has a split pin which can be a bugger to get out then the whole hub is pulled off and the disks can be unbolted from the hub carrier before new discs fitted as I say not technically difficult if you have the knack and tools to undo the large nut.
As always with brakes or steering indeed any safety related system if you’re not 100% confident please take it to a dealer not only can it work out cheaper in the long run it’s also far safer for you and yours.
BR
Colin
