Change Manual Execution To Automatic Execution

I have this codes which will only trigger if I manually execute it. What do I need to do to trigger it automatically whenever the worksheet change.

Below is the codes:

Sub Risk_Color()

Dim c As Range, myFontCol As Integer, myCol As Integer

For Each c In ActiveSheet.Range("f7:g20000")
myFontCol = xlAutomatic
myCol = xlNone
Select Case c.Value
Case Is = 1, 2, 3
myCol = 34
Case Is = 4, 5, 10, 20: myCol = 43
Case Is = 30, 40, 50: myCol = 6
Case Is = 70, 100, 140, 150
myCol = 5
myFontCol = 2