What should I do if a child has a high fever of 40 degrees? Sudden high fever of over 40 degrees

Patient's question:

What should I do if a child has a high fever of 40 degrees? Sudden high fever of over 40 degrees

Doctor's answer:

Please ask if my daughter is two and a half years old now, with a fever of 38.2 degrees, but she doesn't want to take medicine, what should I do? Is 38.2 degrees a very serious fever? How to treat it?