Modify Disk Size Allocated to Hyper-V VM
Open Hyper-V Manager (Contorl Panel > Administrative Tools)
Shut Down the VM you would like to modify.
Right click on the VM you would like to modify and go to settings.
Navigate to the Hard Drive Tab and click on Edit in the Virtual Disk Section.
Select Expand Then Next
Enter the new value for your virtual disk and click Next.
Finish by booting the VM back up.