Reaching your storage limit, this page will help you when that happens.
There are several things you can do to free up some space:
The Home Assistant database can get huge!
Luckily there is a tool you can use to purge the contents of the database
Open the Home Assistant UI and go to Settings > System > Backups, here you will see all your backups, these can be downloaded and placed somewhere safe. When you have done that, you can delete them in the UI and it will free up some space for you.
Add-ons can take a lot of space, not just the add-on itself but also their data.
Open the Home Assistant UI and go to Settings > Add-ons in the sidebar. Here you will see all your installed add-ons, maybe you have some that you no longer use, if you do those can be uninstalled to free up some space.
If all else fails, you need to expand your storage.
If you are running Home Assistant as a VM, look at the documentation for your hypervisor on how to expand disks for virtual machines. Home Assistant will auto-expand to use the newly added space.
If you are not running a VM, you need to replace your storage medium (typically, this will be an SD card). You can use backups to quickly restore your Home Assistant installation on a new storage medium.