Repartitioning a VPS after an upgrade

Job ID: 33623907

Budget: $10 – $30 USD

so i paid for more storage on a VPS on OVH.com
from 160GB to 320GB
I need to expand the disk partition to reflect the new size (without loosing my data).
My problem is when i try to unmount the disk it keep saying " /dev/sdb1: not mounted "
Related categories: System Admin Linux VPS