I am doing this on proxmox

1) login to the proxmox server

2) cd to the disk you need to expand

cd /var/lib/vz/images

3) Increase the disk size

qemu-img resize diskimage.zzz +[size in GB you want to expand]G

4) boot your VM with gparted or partition magic live iso

5) expand the volume to the new size

6) reboot the VM normally

7) run command

8) note the "VG NAME" 9) run
lvextend -L+[size in GB you want to expand]G /dev/{insert VG NAME]/root
10) Done!