Here is the delete macro that you can Assign. Test on backup copy as usual.
Sub Del12Months()
Dim i As Integer, j As Integer, r As Range, c As Range
Application.EnableEvents = False
Application.ScreenUpdating = False
Application.Calculation = xlCalculationManual
With Worksheets("Year Planner")
' With ActiveSheet 'Used for quick testing on copies of sheet1 as activesheet.
For i = 7 To 52 Step 15
' 1st row of 3 months menus
Set r = Range(.Cells(i, "A"), .Cells(i, "W")).Offset(3)
For j = 0 To 10 Step 2
Set c = r.Offset(j)
c.ClearContents
Next j
Next i
End With
Application.EnableEvents = True
Application.ScreenUpdating = True
Application.Calculation = xlCalculationAutomatic
End Sub