I wolud like to modify my Kenmore chest freezer to...

Question

I have KenmoreElite chest freezer model # 253 16092100 and there is a digital display in handle, capable of -10 F to -20 F. I want to modify to -40 F .I think it need R404A refrigerant and special thermostat. I don’t know it is correct or not. I’m wondering what type of thermostat can be used and where I can buy it. I need some advices please.
Sam