• backup the contents of /home

> tar -czvf /root/home.tgz -C /home .

• test the backup

> tar -tvf /root/home.tgz

• unmount home

> umount /dev/mapper/centos-home

• remove the home logical volume

> lvremove /dev/mapper/centos-home

• recreate a new 400GB logical volume for /home,format and mount it

> lvcreate -L 400GB -n home centos
> mkfs.xfs /dev/centos/home
> mount /dev/mapper/centos-home

• extend your /root volume with ALL of the remaining space and resize (-r) the file system while doing so

> lvextend -r -l +100%FREE /dev/mapper/centos-root

• restore your backup

> tar -xzvf /root/home.tgz -C /home

• check /etc/fstab for any mapping of /home volume. IF it is using UUID you should update the UUID portion. (Since we created a new volume,UUID has changed)

Copied from:

http://serverfault.com/questions/771921/how-to-shrink-home-and-add-more-space-on-centos7