Apps do take up a lot of space, as do other files as well. You can try moving Photos, Videos, Music and other such files to your SD card (if you have one) as the phone can take a card up to 32 GB. That should free up a lot of space for you.
You can also try cleaning up what is being left on the phone by your apps. There are some really good, and free, cleaner apps out there. Me I like "Clean Master", but there are many to choose from.
Now if you are wanting to move apps over to the card, well that takes more work. You would first need to have, or be able to upgrade to Android "Marshmallow". Then you would need to have a device not restricted by the manufacturer (which does happen) and lastly the instructions I am including below. If they don't work for you, or you are missing the stuff on one of the steps to set it up, then you probably have a restricted device.
How to turn the "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 (making the cards data only readable by that device).
1. Go to device “Settings”, then select “Storage”.
2. Select your "SD Card", then tap the “three-dot menu“ (top-right), now select “Settings” from in there.
3. Now select “Format as internal”, and then “Erase & Format”.
4. Your SD Card will now be formatted as internal storage.
5. Reboot your phone.
NOTE: If you don't reboot the phone, many things may not work correctly, so make sure you do.
How to turn the "External" SD card into "Internal" storage on "Nougat".
IMPORTANT NOTE: Be sure you start with a blank SD card. When the card is converted to "Internal" storage, it will be formatted (wiped) and encoded (making the cards data only readable by that device), so anything on it prior would be gone.
1. Go to "Settings", and then select "Storage & USB".
2. At the bottom of the list you should see the SD card's details, including the option to format it and make it "Internal" storage.
3. Once this is done, reboot the device and you can start running things from the card.
If you don't reboot the phone, some things may not work correctly, so make sure you do the reboot.