You cannot "downgrade" your official dashboard version easily; this usually requires hardware modification (RGH/JTAG). Wonderful PCB install Aurora on a modded console, or are you looking for official themes for a standard Xbox 360? How to JTAG Your Xbox 360 and Run Homebrew - Instructables 22 Feb 2010 —
Extract the Aurora folder to the root of your USB. It should look like E:\Aurora\default.xex . xbox 360 custom dashboard