It depends on what you are trying to download to the card. If you are just trying to download things like music, images, etc., then you would have to change the settings in the app you are downloading those files through. Now if you are wanting to download apps themselves directly to the card you would 1. Need to be using Android "Marshmallow" or able to upgrade to it, and 2. Have a phone that does not restrict the ability to change the card to "Internal" storage. Try the following instructions. If it works for you, then you are good. If your phone doesn't have the options (and is running "Marshmallow") then it was restricted by the manufacturer.
How to turn external SD card into internal storage on "Marshmallow".
NOTE: Please be...