umount /home does not work

I trying to merge my separate /home partition with my / partition in linux mint 13. I was told to umount /home, mount it on a different location and copy the contents to the /home directory on the / partition. I have tried, but I cannot umount /home. When I try to do so, I get a message: umount: /home device is busy (which processes use this device can be possibly be found with lsof or fuser) How can I unmount my /home and mount it on a separate location (/dev/sda2/mnt/home) to be able to copy the contents to /home?