If you are using IIS for hosting your application, then the default upload file size is 4MB. To increase it, please use this below section in your asp.net web.config -

<configuration>
<system.web>
<httpRuntime maxRequestLength="1048576" />
</system.web>
</configuration>
For IIS7 and above, you also need to add the lines below:

<system.webServer>
<security>
<requestFiltering>
<requestLimits maxAllowedContentLength="1073741824" />
</requestFiltering>
</security>
</system.webServer>
Note:

maxRequestLength is measured in kilobytes
maxAllowedContentLength is measured in bytes