Increase linux disk space?

[g4143]

Filesystem Size Used Avail Use% Mounted on
/host/ubuntu/disks/root.disk
17G 11G 4.7G 70% /
tmpfs 1.8G 0 1.8G 0% /lib/init/rw
varrun 1.8G 216K 1.8G 1% /var/run
varlock 1.8G 0 1.8G 0% /var/lock
udev 1.8G 152K 1.8G 1% /dev
tmpfs 1.8G 84K 1.8G 1% /dev/shm
/dev/sda5 103G 18G 85G 18% /host
lrm 1.8G 2.2M 1.8G 1% /lib/modules/2.6.28-15-generic/volatile
/dev/sdb1 996M 85M 911M 9% /media/360USBDRIVE

Well whats on this partition - /dev/sda5? Its 103G and mounted on /host