Your files in MMC are stored in multiple (disk) blocks.
So if you format using 16K block, the space used will be 16K even though your file is just 1K.
If you buy MMC, it is usually pre formatted with 16K block. Therefore alot of space is wasted as most installed program files are usually less than 2K.
You will need a card reader to do this:-
1. Connect card reader and copy all your files in the MMC to computer disk.
(Make sure you set the show all/hidden/os files to "on")
2. Do a format of the MMC using command line "format" and use the /A=size option.
Alternative, you can use the Disk Management in Adminstrative Tools to format.
Make sure you select FAT. For 256MB MMC, smallest block you can use is 4K, 128MB is 2K, 64Mb is 1K and 32MB is 512B.
(Note: You cannot use the phone "format MMC" to do this as the format just clear the allocation table and does not change the block size)
3. Copy back all files to MMC.
Now you will find that you will have more space.
256mb MMC you will get about back 30+ mbs