Well if the information I am finding is correct, your phone runs on an older version of Android so it would not be possible. Unless you can find a way to upgrade the phone to "Marshmallow", then (as long as the manufacturer hasn't restricted the option to make this change, some do) you can try the following.
How to turn external SD card into internal storage on "Marshmallow".
NOTE: Please be sure you start with a blank SD card. It needs to be blank because when the card is converted to "Internal" storage, it will be formatted (wiped) and encoded (making the cards data only readable by that device).
1. Go to device “Settings”, then select “Storage”.
2. Select your "SD Card", then tap the “three-dot menu“ (top-right), now select “Settings” from in there.
3. Now select “Format as internal”, and then “Erase & Format”.
4. Your SD Card will now be formatted as internal storage.
5. Reboot your phone.
There is also
this great tutorial you can use to make the SD card your default storage location.
NOTE: If you don't reboot the phone, many things may not work correctly, so make sure you do.