<configuration>
    <system.web>
        <!-- This will handle requests up to 50MB -->
        <httpRuntime maxRequestLength="51200" timeout="3600" />
    </system.web>
</configuration>

<!-- IIS Specific Targeting (noted by the system.webServer section) -->
<system.webServer>
   <security>
      <requestFiltering>
         <!-- This will handle requests up to 50MB -->
         <requestLimits maxAllowedContentLength="52428800" />
      </requestFiltering>
   </security>
</system.webServer>

source: forums.asp.net