Example showing how I resized an Ubuntu server from 10GB to 40GB
I had resized with VirtualBox (like increasing physical medium)

# /dev/sda2 looks like our main drive mount (its full)
$ df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            969M     0  969M   0% /dev
tmpfs           200M  968K  199M   1% /run
/dev/sda2       9.8G  9.3G  372K 100% /
tmpfs          1000M     0 1000M   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs          1000M     0 1000M   0% /sys/fs/cgroup
/dev/loop0       94M   94M     0 100% /snap/core/8935
/dev/loop1       15M   15M     0 100% /snap/aws-cli/130
/dev/loop2       90M   90M     0 100% /snap/core/8268
tmpfs           200M     0  200M   0% /run/user/1000

# lsblk command displays information about the block devices attached
# that disk has two partitions (partition 2 is the main storage space)
$ lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
loop0    7:0    0 93.8M  1 loop /snap/core/8935
loop1    7:1    0   15M  1 loop /snap/aws-cli/130
loop2    7:2    0 89.1M  1 loop /snap/core/8268
sda      8:0    0   40G  0 disk
├─sda1   8:1    0    1M  0 part
└─sda2   8:2    0   10G  0 part /
sr0     11:0    1 1024M  0 rom

# grow second partition to fill the HD space available
$ sudo growpart /dev/sda 2
CHANGED: partition=2 start=4096 old: size=20965376 end=20969472 new: size=83881951,end=83886047

# now it shows the partition has grown
$ lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
...
sda      8:0    0   40G  0 disk
├─sda1   8:1    0    1M  0 part
└─sda2   8:2    0   40G  0 part /
...

# but the mount has not scaled because we need to extend file system
$ df -h
Filesystem      Size  Used Avail Use% Mounted on
...
/dev/sda2       9.8G  9.3G  372K 100% /
...

# resize2fs will  resize ext2, ext3, or ext4 file systems, mounted or unmounted
# extend it
$ sudo resize2fs /dev/sda2
resize2fs 1.44.1 (24-Mar-2018)
Filesystem at /dev/sda2 is mounted on /; on-line resizing required
old_desc_blocks = 2, new_desc_blocks = 5
The filesystem on /dev/sda2 is now 10485243 (4k) blocks long.

# DONE!
$ df -h
Filesystem      Size  Used Avail Use% Mounted on
...
/dev/sda2        40G  9.3G   29G  25% /
...