Sometimes, there are many URL embedded in our Joomla websites, which becomes impossible to each and every thing and change from HTTP to HTTPS.
So, there are two steps to be done, in order to force all non-secure HTTP links in a Joomla website to secure- HTTPS links automatically.
Step 1 : Goto Admin Backend >> Global Configuration >> Server >> Force SSL >> Entire Site
Step 2 :Edit the .htaccess file in the website root folder and place this below code on the bottom of the htaccess file.