Well, it is going to depend on what Android version your phone is using. If it is using anything older than "Marshmallow" then you won't be able to to it. However, if it already is using, or you can upgrade it to, "Marshmallow" then you may be able to make the SD card the default download location, and move apps to it.
I say 'may' because some manufacturers have restricted this option on some of their devices, no matter if it is running "Marshmallow" or not. So you won't know until you try.
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...