When you upgrade the VM and increase available RAM and/or CPU, these changes are not reflected in Health Monitor. The old values of the hardware capacity are still shown.
New hardware configuration values are not automatically re-calculated by Health Monitor.
Run the following command to make Parallels Plesk Panel Health Monitor recognize recent hardware configuration changes:
"%plesk_bin%\php.exe" -d auto_prepend_file="" "%plesk_dir%\admin\plib\scripts\setup-health-monitor.php"