Samsung Galaxy S4 Lags and Stops on Responding

Hi, I have a Samsung S4 Smartphone and I really like it. It is packed with so many remarkable features. It was working fine at first and I really enjoyed it. But lately, I am having trouble since it keeps on lagging. It will randomly hangs up and will stop on responding. I will turn it off and on to make it work again. I already tried to reset my phone and check on the memory. No luck! What can I do to fix this issue? Thanks.
