The best way is to make the conversions on the Arduino sketch.
This is the formula to convert to F
tempF = tempC x 1.8 +32
So, you need to change the following line:
readings["temperature"] = String(bme.readTemperature());
readings["temperature"] = String(bme.readTemperature()*1.8 + 32);
Proceed similarly to convert pressure.
document.getElementById("temp").innerHTML = myObj.temperature;
You should have
document.getElementById("temp").innerHTML = myObj.temperature*1.8 +32;
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