On cloud servers, once you upgrade disk, you will need to resize the filesystem. On Linux ext4 file system, you can do this with command resize2fs.
To resize filesystem on /dev/sdb, run
root@leonestage:~# resize2fs /dev/sdb
resize2fs 1.44.1 (24-Mar-2018)
Filesystem at /dev/sdb is mounted on /mnt/HC_Volume_2899894; on-line resizing required
old_desc_blocks = 2, new_desc_blocks = 3
The filesystem on /dev/sdb is now 10485760 (4k) blocks long.
Here the full disk is used as file system with NO partition. If you have partion, you need to specify partition number like /dev/sdb1