Open your registry and find the key below.
Create a new DWORD value called "DiskSpaceThreshold" and set it to the percentage of free disk space remaining before an alert is sent.
Restart Windows for the change to take effect.
System Key: [HKEY_LOCAL_MACHINE\System\CurrentContro
Type: REG_DWORD (DWORD Value)
Value: 0 - 99 percent (Default is 10