To force httpS on all pages (secure pages) you have to have a SSL / security certificate installed on your website. This is generally done by your hosting company. I personally buy mine from godaddy.com, but your host may offer them as well.
Then you need to do 2 things.
1) In your Sytist admin click Settings in the main menu. Then underneath the left menu click edit .htaccess file.
Look for these 3 lines
RewriteEngine On
RewriteCond %{HTTP_HOST} ^(YOUR-DOMAIN.com)$ [NC]
RewriteRule ^(.*)$ http://www.%1/$1 [R=301,L]
If you have those 3 lines in your .htaccess file, replace them with the following. If you don't have those 3 lines then just add the following (replacing YOUR-DOMAIN.com with your domain ... like picturespro.com)
RewriteEngine On
RewriteCond %{SERVER_PORT} 80
RewriteRule ^(.*)$ https://www.YOUR-DOMAIN.com/$1 [R,L]
Save.
2) Next you have to edit the sy-config.php. You can do this in your Sytist admin by click Settings in the main menu, then underneath the left menu click "edit config file".
Change this line:
$setup['url'] = "http://".$_SERVER['HTTP_HOST']."";
TO:
$setup['url'] = "https://".$_SERVER['HTTP_HOST']."";
Notice we are adding a s to http.
And save.