Please follow the steps below to modify the image:

1.  On the Web server, navigate to [INSTALL_DIRECTORY]\bbappfx\vroot\browser\clientbin\Images\brand\bbec
2.  Rename bbec.webshellbanner.png to .old or another extension/name of your choosing (to preserve the original)
3.  Copy the new PNG image file into [INSTALL_DIRECTORY]\bbappfx\vroot\browser\clientbin\Images\brand\bbec and rename it to bbec.webshellbanner.png
4.  Recycle the application pool