Fever can be reduced by following means --
Sponging with cool water to the patient's skin or cool water bath will reduce the fever considerably. Many prefer ordinary tap water than cool water. But sponging should be done all over the body as most of people do on forehead and armpits.
Anti-pyretics can also be given. Actaminophen (paracetamol) or ibuprofen may be used on the advice of a doctor. Aspirin may also be used in adults but should be avoided in children because it may cause Reye's syndrome in them.
A fever may cause dehydration so give plenty of fluids to the patient.
However remember: It needs to be ascertained what the cause of a fever is, so consult a doctor about it.