I developed a website. It has been hosted in google cloud platform.I was required to change the banner of picture of the home page of website. I changed in server but It showed previous banner picture so I cleared the cache by following command
sudo touch /var/cache/mod_pagespeed/cache.flush
Subsequently I refresh the web page then the picture was changed as new picture. But after few hours or when i click another page and again come to this page The previous(old) picture again replaced the new picture. What can I do to solve this problem and what is the reason?