Unfortunately since that device is not running the newest OS, "Marshmallow", it is not possible to make the SD card read as "Internal" which is what is needed to make it the default storage, rather than the standard "External".
Although I don't know of a way to update it that far, but if you can update the device to "Marshmallow" then you might be able to make the change. However you would need to start with a blank SD card. Why? Because when the change is made, the card is formatted and encrypted to work with only that device. Alas, that only matters if you can update to "Marshmallow" and can get the device to accept the card change (some devices just won't).
The only other option I know of is to root the device. That I cannot...