Expand volume size in Ubuntu 18.04 VPS | Xen

I got this VPS from my friend and want to expand root volume because it’s too small.

root@MyServer:~# df -h
Filesystem                   Size  Used Avail Use% Mounted on
udev                         3.9G     0  3.9G   0% /dev
tmpfs                        801M  460K  801M   1% /run
/dev/mapper/ubuntu--vg-root  8.3G  2.9G  5.1G  37% /
tmpfs                        4.0G     0  4.0G   0% /dev/shm
tmpfs                        5.0M     0  5.0M   0% /run/lock
tmpfs                        4.0G     0  4.0G   0% /sys/fs/cgroup
/dev/xvda1                   472M  133M  316M  30% /boot
tmpfs                        801M     0  801M   0% /run/user/0

fdisk -l show me there’s another disk xvdb

root@MyServer:~# fdisk -l
Disk /dev/xvdb: 70 GiB, 75161927680 bytes, 146800640 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes


Disk /dev/xvda: 10 GiB, 10737418240 bytes, 20971520 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x5285bf7f

Device     Boot   Start      End  Sectors  Size Id Type
/dev/xvda1         2048   999423   997376  487M 83 Linux
/dev/xvda2      1001470 20969471 19968002  9.5G  5 Extended
/dev/xvda5      1001472 20969471 19968000  9.5G 8e Linux LVM


Disk /dev/mapper/ubuntu--vg-root: 8.6 GiB, 9172942848 bytes, 17915904 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes


Disk /dev/mapper/ubuntu--vg-swap_1: 976 MiB, 1023410176 bytes, 1998848 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Is there anyway to expand my root volume using that 70GB of xvdb? I’m so new to Ubuntu 🙁