Also answered on Casio user forum:
http://www.originalz.com/casio/casio_bbs/ The built in 'song sequencer' can have 6 tracks (11 to 16), with track 11 also holding the 'rhtyhm' information for tracks 5 thru 10. To delete a 'track' (11 thru 16), press the song memory 1 time (to the 'play' display). You use the 'big' registration buttons...to select the track (11 thru 16) that you want to 'delete'. The button labled 'bank', is track 11...and so on, to the button marked 'store' that is track 16. Pressing these buttons will cause the corrosponding track to flash. Press the 'yes' button to each prompt, to finish the delete. Yes you can remove one SMF file from the group.
If you want to remove SMF files from the Casio memory, Press the Transpose button. Cursor down to 'DelSMF'. Press 'yes'. The first song's name will display. Use the 'right/left' cursors to move thru the list. When you see one you want to delete...press the 'down' cursor. Answer 'yes' to the prompt....and the SMF will be deleted. The SMF files are loaded by 'date'....meaning the most recent additions are placed at the end of the list. So, if you want to arrange the order of play...you control that by the order you load the SMF files into Casio memory.