Unfortunately, Android KitKat took away the easy route to that from the Settings menu but it can be done, with some patience. You could start by rooting the machine but it's possible you can find Root File Manager in the Play Store and run that without rooting. That should open up the file structure so you can see the external SD card.
Alternatively, you could download Terminal Emulator from the Store and use some simply command line entries to navigate your way. When you open the teminal you're at a black form where the Command Line lives. At the prompt type
ls
and hit Enter. That shws you the LiSt of folders and files. sd card might be in the list and if it does, type
cd sdcard
and hit Enter. You've used Change Directory...