Echo will be more in hotter day or cooler day? why?

Echo is the reflection of sound of surfaces, and occurs a all temperatures. So the term 'More echo' is ambiguous. I assume that you are asking about the the time lag between the original sound and the echo, and therefore its discernibility.   

The answer to your question then becomes a cooler day. This is because the the speed of sound is lesser on a cooler day and therefore there will be a greater time lag between the original sound and the echo.