D drive is your backup partition, and cannot be easily edited. It is secured so that files may not be easily edited so that it will remain clean of viruses and allow for a smooth backup if necessary. There shouldn't be any files inside of it that you need to clean up.
If you wish to use it to restore your system files, restart your computer and as it's booting it should say something somewhere to the likes of press whatever to open up the recovery manager... I think it's usually F12.