Try deleting some stuff so you can then download a file manager,say Comand Manager,then wiew the files and delete the useless ones

You can remove apps you don't use, you can delete any downloaded files you may have, and you can empty the cache from apps. (You'll have to do each app individually, in the apps setting.

You can also, probably, plug in an sd card or external usb hard drive and use that as more space.