If you wish to unmount your root partition and modify the filesystem parameters, get rescue software for Linux.
Use the rescue software, then use tune2fs to make the modifications.
To detach a previously mounted file system, use either of the following variants of the umount command:
When a file system is in use (for example, when a process is reading a file on this file system), running the umount command will fail with an error.
To determine which processes are accessing the file system, use the fuser command in the following form:
fuser -m directory
For example, to list the processes that are accessing a file system mounted to the /media/cdrom/ directory, type: