Formatting Changing without Erasing the data on an External Harddisk

The format of my Ext. HD is Mac OS Extended (Case-sensitive, Journaled); it was sort of default when I first used it.

But now I want to have it changes to Mac OS Extended (Journaled), as I guess I won't be needed to enter the password for authentication every time I copy folders on it.

Is there any way I could format my Ext. HD without erasing the folders that are already in the HD? As it would be quite clumsy to copy the folder back and forth.

Thanks a lot in advance!

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