Why entropy decreases with the increase in temperature?

Ans.
dS =  dQ / T

Entropy is inversely proportional to the temperature. Thus on increasing temperature the entropy decreases.

One more thing to remember about entropy is for non reversible non cyclic processes entropy is always positive.   

Must Watch this video for complete understanding of Entropy. 
You will understand after watching this video; 
 - Entropy of substance at different states 
 - Entropy of surrounding or universe
 - " Tendency of nature is always to increase the entropy. "