For your .NET Website, this is the simple way below, just update your web.config with the following:

<system.webServer>
    <httpProtocol>
      <customHeaders>
        <add name="Strict-Transport-Security" value="max-age=31536000" />
      </customHeaders>
    </httpProtocol>
    <rewrite>
      <rules>
        <rule name="HTTPS force" enabled="true" stopProcessing="true">
          <match url="(.*)" />
          <conditions>
            <add input="{HTTPS}" pattern="^OFF$" />
          </conditions>
          <action type="Redirect" url="https://{HTTP_HOST}{REQUEST_URI}" redirectType="Permanent" />
        </rule>
      </rules>
    </rewrite>
  </system.webServer>
</system.webServer>

If you want to do it with IIS 8

• Open IIS 8
• Click “Add Rule(s)”
• Blank rule

• Name: HSTS Redirect
• Requested URL: Matches the Pattern
• Using: Regular Expressions
• Pattern: (.*)
• Ignore case: Checked

Conditions

• Logical grouping: Match all
• Click “Add”
• Condition input: {HTTPS}
• Check if input string: Matches the Pattern
• Pattern: ^OFF$
• Ignore case: Checked

Action

• Action type: Redirect
• Redirect URL: https://{HTTP_HOST}/{R:1}
• Append query string: Checked
• Redirect type: Permanent (301)