All files are backed up as incremental backups meaning your first backup will be a full backup and each backup afterwards will be incremental backups, which mean that only files that have changed will be backed up. If you selected to retain backups for a week, then once the full backup is deleted, another full backup will be made, and after that, each backup will be incremental. Our backup service is smart enough to understand the difference between a full backup and incremental backups, so you need not worry. This new service was designed like this to maximize the amount of space before files are deleted.