From this screen you can see the size of your current settings back up; the total storage space you have available on OneDrive and when the date/time of the last backup.
You can tap the Back up now button to initiate a manual backup if you want to but this backup happens automatically when changes are made to you device settings.
Next you can turn off those automatic backups and choose to do it manually at all times.
Then you can turn off individual apps from backing up their settings from this device as well.
Finally, you can go online to OneDrive and remove those backups that are no longer required.