NWBC - UI Theme designer

Hi Experts,

I would like to customize the initial login screen for the user when the user logins into the NWBC system.

I have gone through below steps.

Tcode:  /IU5/THEME_DESIGNER

then selected the "SAP GOLD REFLECTION" theme to edit and create a new theme using it as a base.

But I was not able to see the Edit button under this...

screen shot attached for your reference.

Please kindly help me how to enable that option so that I create custom theme's.

Thank You.