TestRail limits the size of uploaded files to a maximum of 256MB. However, PHP is usually configured to limit the upload file size to just a few MBs in the default configuration. You can easily increase this limit by changing two settings in the PHP.ini configuration file:
This would increase the file upload limit to 64MB. After changing the configuration settings and saving the PHP.ini file, you should also restart the web server service (either Apache or IIS) to apply the new settings.