To redirect your http site to https, you can input the following code into your .htaccess file under public_html. Make sure to upload the file into the correct directory.
Redirect your http site to https:
# First rewrite to HTTPS:
# Don’t put www. here. If it is already there it will be included, if not
# the subsequent rule will catch it.
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
# Now, rewrite any request to the wrong domain to use www.
RewriteCond %{HTTP_HOST} !^www\.
RewriteRule ^(.*)$ https://www.%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
NOTE: We do not recommend editing your .htaccess files without professional assistance. A single wrong line in the .htaccess files may affect your whole website.
To install SSL certificate for your website, you may refer to our article about Secure website with SSL.