Try going into "settings" then "Storage" and change the default write disk to the "SD card".
NOTE: Before you try this (if the option is in there), you may want to back up anything that is on the card, because making this change could cause the SD card to be formatted when the change is made, and you would lose the data.
If this option is not there, there is no way to do this on your device, short of rooting it. Many devices running older OS's can't do it. I personally wouldn't recommend rooting.