Cannot change default on my Samsung galaxy Young

Solution
I am assuming you mean change it from downloading apps to the "Internal" storage to the SD card? If that is the case you will need to have a phone that is running at least Android "Marshmallow" and also that was not restricted by the manufacturer. Yes they actually do that. If it was/is restricted, then the following instructions will not work for you.


How to turn the "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...
I am assuming you mean change it from downloading apps to the "Internal" storage to the SD card? If that is the case you will need to have a phone that is running at least Android "Marshmallow" and also that was not restricted by the manufacturer. Yes they actually do that. If it was/is restricted, then the following instructions will not work for you.


How to turn the "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.

NOTE: If you don't reboot the phone, many things may not work correctly, so make sure you do.


How to turn the "External" SD card into "Internal" storage on "Nougat".

IMPORTANT NOTE: Be sure you start with a blank SD card. When the card is converted to "Internal" storage, it will be formatted (wiped) and encoded (making the cards data only readable by that device), so anything on it prior would be gone.

1. Go to "Settings", and then select "Storage & USB".
2. At the bottom of the list you should see the SD card's details, including the option to format it and make it "Internal" storage.
3. Once this is done, reboot the device and you can start running things from the card.

If you don't reboot the phone, some things may not work correctly, so make sure you do the reboot.

 
Solution