As you know there are many settings within IIS. One of these settings is called the maxRequestLength, which prevents files over 4mbs from being uploaded.
Adjusting the following setting should correct the issue for you:
1. Navigate to IIS
2. Select your site
3. Open Configuration Editor
4. Select system.web
5. Select httpRuntime
6. Look for maxRequestLength:
In the example above, the maxRequestLength is set for 4096 which equals 4MB. By setting it to 300000, this would be similar to the equivalent of 300 MB. Please adjust the size accordingly.