Extend logical volume to occupy the rest of the free space

Check that nothing is locking the partition:-

 lsof /opt/  

Unmount the partition:-

 umount /opt  

Extend the partition:-

 lvextend -l +100%FREE /dev/mapper/vg_root-lv_opt  

Check the filesystem:-

 e2fsck -f /dev/mapper/vg_root-lv_opt  

Resize the filesystem:-

 resize2fs -p /dev/mapper/vg_root-lv_opt  

Check the filesystem:-

 e2fsck -f /dev/mapper/vg_root-lv_opt  

Remount the partition:-

 mount /opt/