Moving block files

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self.Bitcoin
I have an up to date version of the blockchain stored on an external drive. I would like to copy it to a different drive (to use it for different purposes on a different device). When I attempt to copy files (using a GUI) I am greeted with the message "You do not have permissions in the destination drive." I assume that I need somehow to use a sudo command but that's about the limit of my knowledge. So answer me like I'm five years old.