You can now change the labels that are attached to file sizes, in either constants or setup:
#constants
styles.content.uploads.filesize.labels = Bytes | KB | MB | GB
# setup
tt_content.uploads.20.filesize.labels = Bytes | KB | MB | GB
More info:
RFC: Feature Request #8487: Enable configuration of filesize labels for CType uploads
http://bugs.typo3.org/view.php?id=8487