[slob]

reuse the collets (unless you find broken ones, which you’ll want to replace)
you want to refit them the same way up as before. You’ll be able to see they’re polished/worn on the inner edge/up from contact with the valve stem and outer edge/down from contact with the shim.
I’d advise using a bit of workshop towel or similar to cover the oil galleries, to prevent any collets disappearing downwards as you’re taking them out. I use a telescopic magnet tool to pick them out, to avoid this happening.
I also use a very small hammer and an aluminium (soft enough not to risk mushrooming the valve tops) drift, to tap the top of the valves once they’re back in to make sure they’re properly seated.