Please give more details like are you using wordpress or is it just html or etc.
You can force https by editing .htaccess file
RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
Change image, css, js etc. files from http to https from code source.
If you are using wordpress you can go to wp-admin -> Settings -> General and change the site url and wp address from http to https and so on.
+1, this is the correct way to force redirects to HTTPS.
Just ensure you don't use RewriteEngine On twice, if Wordpress, your file should 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]
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
</IfModule>
# END WordPress
