Please follow below steps to redirect http to https mode:
1. Please make sure IIS rewrite module is installed on your IIS service, it is default module for IIS 7.5 and onwards.
2. Edit web.config
2a. Between <system.webServer> tag
eg:
<system.webServer>
</system.webServer>
insert the IIS rewrite rules as below:
<system.webServer>
<rewrite>
<rules>
<rule name="HTTP/S to HTTPS Redirect" enabled="true" stopProcessing="true">
<match url="(.*)" />
<conditions logicalGrouping="MatchAny">
<add input="{SERVER_PORT_SECURE}" pattern="^0$" />
</conditions>
<action type="Redirect" url="https://{HTTP_HOST}{REQUEST_URI}" redirectType="Permanent" />
</rule>
</rules>
</rewrite>
</system.webServer>
3. To edit config/shop$config.asp and <your_admin_folder>/config/shop$config.asp
3a. to modify xmysite and xssl as https://www.yourdomain.com