Maximum request length exceeded, IIS 8.5

Question

I am calling a web request from my Delphi code to upload a file (size: 3 to 6 MB) but I am getting the error:

Maximum request length exceeded.

How do I fix this?

Update: I have updated the web.config file with the below code but I am still getting the same error. My server is IIS 8.5 on HostGator. I have also asked the HostGator team to increase my file size from server end.

<configuration>
  <system.web>
      <webServices>
          <protocols>
              <add name="HttpGet"/>
              <add name="HttpPost"/>
          </protocols>
      </webServices>
    <compilation debug="true" targetFramework="4.7.1" />
    <httpRuntime targetFramework="4.7.1" />
  </system.web>
<system.webServer>
    <security>
        <requestFiltering>
            <requestLimits maxAllowedContentLength="268435456" />
        </requestFiltering>
    </security>
</system.webServer>
</configuration>

I have tried using this:

<httpRuntime maxRequestLength="51200" />

but I got:

internal server error