Themes can quickly consume up storage space because themes can include images, sounds and icons. Remove themes you're not using. See Deleting a theme in
Keep only the most recent data in your apps and files that you often need to use. You can back up your other data and files.
Uninstall apps that you've downloaded if no longer need them. See
Uninstalling an app.
Preinstalled apps can be disabled when you're not using them. See
Disabling an app.
Storage screen, tap
Free Up Space. The phone then checks the phone storage and then suggest items that you may want to delete.
Third-party apps that you've downloaded and installed can be moved to the storage card if you've set up the card as internal storage. See
Moving apps and data between the built-in storage and storage card and
Moving an app to or from the storage card.