Is there any way without rooting the device? My device is a Sony Xperia C4.
Yes, you can use adaptable storage to do this. This means that your SD card with merge with your internal storage and display itself as one big SD card. This is really nice if you need extra storage, but things can go crazy if you pull your SD card out of your phone as it's used as internal storage.
Just make sure NOT to pull out your SD card from your phone if you decide to enable this.
You can enable it in 2 ways:
adb shell sm set-force-adoptable true
Go to Settings -> Storage -> SD Card -> Format as internal