Redirect All HTTP requests to HTTPS via .htaccess

Edit the file .htaccess that is in your WordPress directory and add these 2 lines:

RewriteCond %{HTTPS} !=on
RewriteRule ^(.*) https://%{SERVER_NAME}/$1 [R,L]

If you use the original .htaccess of WordPress, then your file must look like this:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
# Rewrite HTTP to HTTPS
RewriteCond %{HTTPS} !=on
RewriteRule ^(.*) https://%{SERVER_NAME}/$1 [R,L]
</IfModule>
# END WordPress