How to increase the max upload file size in ASP.NET?

This setting goes in your web.config file. It affects the entire application, though... I don't think you can set it per page.

<configuration>
  <system.web>
    <httpRuntime maxRequestLength="xxx" />
  </system.web>
</configuration>

"xxx" is in KB. The default is 4096 (= 4 MB).

For IIS 7+, as well as adding the httpRuntime maxRequestLength setting you also need to add:

  <system.webServer>
    <security>
      <requestFiltering>
        <requestLimits maxAllowedContentLength="52428800" /> <!--50MB-->
      </requestFiltering>
    </security>
  </system.webServer>

Or in IIS (7):

• Select the website you want enable to accept large file uploads.
• In the main window double click 'Request filtering'
• Select "Edit Feature Settings"
• Modify the "Maximum allowed content length (bytes)"