This command lets you change the passphrase of an encrypted disk image. This is a fast operation that does not require copying the whole file or use lots of temporary disk space. To change the passphrase and the format, use the Convert Image/Archive… command.
On Mac OS X 10.10 and later, DropDMG will first prompt for the new passphrase, and then the system will prompt for the old one. On earlier versions of Mac OS X, the system will first prompt for the old passphrase and then the new one.
When choosing the file, you can hold down the Command or Shift key to change the passphrases of multiple images at once.