The following VBA code shows you how to get a handle on a raster layers renderer:
Public Sub test()
' Get document
Dim pmxd As IMxDocument
Set pmxd = ThisDocument
' Get map
Dim pmap As IMap
Set pmap = pmxd.FocusMap
' Get first layer (assumed to be raster)
Dim pLayer As ILayer
Set pLayer = pmap.Layer(0)
' QI into rasterlayer
Dim pRasterLayer As IRasterLayer
Set pRasterLayer = pLayer
' Get renderer
Dim pRasterRenderer As IRasterRenderer
Set pRasterRenderer = pRasterLayer.Renderer
' Test renderer type and report
If TypeOf pRasterRenderer Is IRasterStretchColorRampRenderer Then
Debug.Print "stretchy!"
Dim pRasterStretchColorRampRenderer As IRasterStretchColorRampRenderer
Set pRasterStretchColorRampRenderer = pRasterRenderer
Debug.Print pRasterStretchColorRampRenderer.LabelHigh
End If
End Sub