To enable HTTPS in all pages of your prestashop website follow this
1. find your .htaccess file (usually in the root folder)
2. open the file ---- >FInd for "RewriteEngine on" if its off make it on
3. Under this write this below code
RewriteCond %{SERVER_PORT} 80
RewriteRule ^(.*)$ https://yoursitename.com/$1 [R,L]
4. Save and upload the file to respective directory
NOTE: Extra rewriteRule may be present under "RewriteEngine on" Ignore do not modify until you understand it fully.