Looks to me the 9000 is a 128MB device, not 256. BlackBerry Bold 9000 - Full phone specifications
If you are trying to upgrade to a newer OS version released for your device model, it will fit on the device, but probably leave you with less free memory than you had before.
Bottom line, the only way I know to interpret the error you posted is that you need to free up some memory. I've given you what tips I know.
You could do a full backup to save your data. If you have paid apps you want to backup, see blackberryfaq.com for directions, but you say you haven't downloaded any apps. After the backup, do a security wipe and select to delete all apps. Then do the upgrade, restore your data, and then decide what apps to restore until your file free is about as low as you dare make it. Posted via BlackBerryForums.com Mobile