Resize vm disk

• Resize disk in the vm's hardware tab using proxmox webUI
• Find disk's name (usually for us sda)
• launch parted parted /dev/sda
• use print  to print the current partition table (replace sda with disk's name)
  
• resize your taget partition with resizepart <PART's ID> 100% 
  
• Finally, quit parted and run resize2fs /dev/sda{PART's ID}

Source :

DON'T DO PART 2 AND 3 
Part 3 is a replacement or part 2.
https://pve.proxmox.com/wiki/Resize_disks