It is the system storage that is getting full, is what that is telling you. Which is the same as the "Internal" storage. Now your phone should be running the "Marshmallow" version of Android. If that is the case, you 'should' be able to turn an SD card into internal storage. Unless Alcatel has restricted it for some reason. Manufacturers do that sometimes.
You do need to start with a "Blank" SD card though. Why? Because when you turn the card into "Internal" storage, it will formate the card and encode it. Erasing any data on it already and making it only usable in that device. So make sure you take anything you have on the SD Card off it. Put it say on a computer or cloud account, until you are done with the change. Then you can...