Unfortunately, since your phone uses an older OS, it isn't possible to set the SD card as default or "Internal" storage. On most phones, prior to those using Marshmallow that is, have it set so that cards can only be used as "External" storage. On Marshmallow, well on most phones using it (as a few manufacturers have decided to still restrict that option even in that OS), you can set your card as internal, so that you can run apps from it, download to it, etc. However some sites and apps still don't always work with this option.
If you can can update your phone to Marshmallow (some phones can, some can't) you might be able to make this option work. If not, then you would have to stick with only putting apps that are movable, videos, photos, etc., on the card.