Best answer by Amy
The fastest way would be to go into Settings > About phone and check the IMEI number. For a device to be dual SIM, you need to have two IMEI numbers (one for each antenna). If you have only one, the device is a single SIM.
Other method would be to check on our website, on the warranty checker with the serial number of the device.
Also, please note that a phone cannot be upgraded from a single to a dual sim device in any way.