How can we upload large files in asp.net

Default size is 4MB set already set machine config but you can override it and increase the size:-

<system.web>
  <httpRuntime executionTimeout="240" maxRequestLength="20480" />
</system.web>

We can also use the <location> tag in web config to get same effect:-

<location path="Upload">
    <system.web>
        <httpRuntime executionTimeout="110" maxRequestLength="20000" />
    </system.web>
</location>