From my.pogoplug.com, simply place your cursor on the desired file or folder. The "abc|" icon will appear next to the file/folder name; click the icon and you will be placed in edit mode. Type in a new name, then click anywhere outside of the edit area to complete the change.
Don’t forget to maintain the file extension:. i.e. if you are renaming a photo (.jpeg), make sure the new file name still has .jpeg at the end.