Delete column based on header row value

I found the following macro in another thread:

Option Explicit
Sub DeleteColumns()
Dim a As Long
Application.ScreenUpdating = False
For a = 15 To 1 Step -1
  Select Case Cells(1, a).Value
    Case "ACTION", "PROVINCE", "TIME", "INTID"
      Cells(1, a).EntireColumn.Delete
  End Select
Next a
Application.ScreenUpdating = True
End Sub

assuming everything is apples to apples, how do you change "For a = 15 To 1 Step -1" to check all columns and not a specified amount?

In other words one spreadsheet might have 15 columns whereas another might have 220.

Thanks!