When you use CameraFTP cloud recording service, you don't need to worry about the storage space. It is unlimited - You just need to make sure that your camera(s) is configured with the correct parameters matching with your subscription plan(s).
Your old footage will be automatically deleted based on your retention days. So your storage will not be full. You also don't need to manually delete any events.
If you want to delete files, you can do so on CameraFTP.com website. From My Cameras page, click the folder icon below your camera thumbnail, you can access the recorded files. To delete files/folders, you need to select them and then click Delete. You will be required to log on as your Camera Admin. A second "Secure Password" is needed to log on as camera admin. ( The secure password is the same as your regular password by default. You can change it to make it more secure. )