You can either configure IIS to handle https by itself, or you can opt to run LemonTree without https and let a reverse proxy handle TLS encryption.
This document describes how to configure IIS for https.
Adding the Binding
In order to access LemonTree over https, you need to add a binding in IIS. This is done in the IIS Manager for your web site:
On the following dialog you should see a binding of type http already. Go to Add... to add a https binding:
Configure the binding as required.
You can now proceed by either disabling the http binding altogether, configuring LemonTreeWeb to require SSL in which case accessing it over http will give an error, or by adding a redirect to https.