By default Raspberry Pi does not allocate enough of your SD card for it to be usable. Out of the box, if you run
sudo apt upgrade, you’ll get a message saying that you don’t have enough disk space. Here’s how to free up more.
Open Terminal or SSH and execute the following command:
sudo raspi-config --expand-rootfs
You might see an error message when running this, but I’ve ignore it and have had no issues.
You’ll find more details on this resize process here.