Backing up question

I have a My Passport Essential 500 GB, I want to backup pictures and movies. I run the sync and it backs up what I wanted. But later when I delete the file from my computer and resync  the passport it gets removed. Is there a way I can remove files from the computer and keep them on the passport?  I have the WD5000ME version without the WD Smartware. I have looked all over this site and have not really found an answer.

Thanks in advance.

Not with the WD Sync.  You will need to either copy and paste your files and folders to the drive directly, or you can use Windows’ Backup utility.