I am currently using Sitecore 6.6. I wonder how to override the display unit from byte to megabyte?
Does it need to change the xml here sitecore\shell\Applications\Files and what class should be overwrote?
I would suggest not to make any change in this as it is out of the box from Sitecore.
If you still want it for a very specific purpose like your Site Manager (Person who add/edit the content of the Site) to see the size in MB or KB then you may add some custom code.