This is a great video done by one of our own, Etherealicer. I think the YouTube has caption function, so you could watch the translation as you go.
My experience is using around 60-70c(150F) hot water, submerged fully for 2-3min, wiggle the SAK to make sure water penetrate inside the scale. Then use a small screwdriver and a blunt knife to pry them out swiftly once out of water.
After removal, I lay those old scales flat and put heavy objects on top to prevent them bending from the heat and prying.
To put on new scales, make sure you have dry out all the water from the knife or finishing your cleaning of the SAK. Best is to put wrap the scales and knife in leather/thick towel, and use a vise to clam it shut. But most original scales you could probably pop it in by sandwiching between heavy book and flat table.