how to transfer wordpress site from http to https
i have recently install wordpress with LEMP on ubuntu 14.04. then i activated cloudflare cdn with flexible ssl.
my ssl is active and i can open my site with https but the problem is the whole sites design is changed and i get this mssgage
Your connection to the site is encrypted, but Google Chrome has detected mixed content on the page. Be careful if you're entering information on this page. Mixed content can provide a loophole for someone to manipulate the page. This content could be third- party images or ads embedded on the page.
i know i have to change my whole site from http to https to solve that issue but how? im kinda newbie to these field so please give me some detail instruction or a tutorial to move my site from http to https will be great.
also please clear me, do i have to do it everytime when i upload an image, plugin, theme or something? or just one time modification will be enough?