How to expand the root disk partition without LVM

I was wondering how to increase the size of a root partition without LVM.

We have a root partition of 21GB in total and another partition with 2TB in total. Ideally, we'd like to keep everything on / and just increase the size, potentially utilizing the disk currently having the /home mount point.

This is on a dedicated server running Ubuntu 18.04 (server) and so GParted isn't an option, unfortunately.

Is it as simple as changing the /etc/fstab to have the mount point of / on /dev/md4?

df -H;

Filesystem      Size  Used Avail Use% Mounted on
udev             34G     0   34G   0% /dev
tmpfs           6.8G  1.3M  6.8G   1% /run
/dev/md3         21G   14G  6.3G  69% /
tmpfs            34G     0   34G   0% /dev/shm
tmpfs           5.3M     0  5.3M   0% /run/lock
tmpfs            34G     0   34G   0% /sys/fs/cgroup
/dev/md2        511M  153M  327M  32% /boot
/dev/md4        2.0T   71M  1.9T   1% /home
/dev/sda1       535M  6.4M  529M   2% /boot/efi
tmpfs           6.8G     0  6.8G   0% /run/user/0

/etc/fstab;

# <file system> <mount point>   <type>  <options>       <dump>  <pass>
/dev/md3        /       ext4    errors=remount-ro       0       1
/dev/md2        /boot   ext4    errors=remount-ro       0       1
/dev/md4        /home   ext4    defaults        1       2
/dev/sda5       swap    swap    defaults        0       0
/dev/sdb5       swap    swap    defaults        0       0
proc            /proc   proc    defaults                0       0
sysfs           /sys    sysfs   defaults                0       0
/dev/sda1       /boot/efi       vfat    defaults        0       0