How to unload a disk in mac os x Mavericks so that you can partition? (failed to unload disk) I want to expand my startup disk space from 25gb to 40gb using this guide: 
http://blog.kyodium.net/2010/11/increase-disk-and-partition-size-in.html

But if I do umount /dev/disk0s2 as the article says then it says the disk is busy. 
If I do diskutil unmount /dev/disk0s2 like the terminal advices then it says it failed to unmount. 

I can't go to disk utility and do this either because then it gives this message: 


That's why I'm using this article that says you need to use the terminal to expand the disk instead and here is what I've tried:
Try booting form external disk:

Create it first with your OS X version.

Attach the USB **boot** drive to the Mac and reboot
Hold down the OPTION key during boot, then select the attached boot drive (typically has an orange icon at the boot menu)
At the boot menu, choose “Disk Utility” (if using an Installer disk, pull down the “Utilities” menu to access Disk Utility)
Go to “First Aid” and verify the disk, then repair if needed
--&gt; Now perform the original task that threw the “Couldn’t Unmount” error