Change Opening Background Step By Step

Hi, everybody, i want to ask about changing opening background. I have installed StepMania5 in Windows 8. I have viewed a sample of theme(Fiesta Ex) which everything like opening background, option button, flow of game (change from menu->gameplay to menu->preview video and tutorial->gameplay), etc has changed. Can you tell me how to custom it all especially opening background step by step?
Because i have search about it, but i just found how to change or create new theme without detail of file inside the folder.
Many thanks for everyone who can help me

Er.....opening background?I never used Fiesta EX theme and knew nothing about it.

Are you meaning Opening Movie?That might be a avi file in theme's folder.Try search '.avi' in it.

And about the details of files....Actually they are customed most by themers.Even a theme that only includes metric.ini in it can be a new theme(XD).So there isn't any instruction about them.

Er.....opening background?I never used Fiesta EX theme and knew nothing about it.

Are you meaning Opening Movie?That might be a avi file in theme's folder.Try search '.avi' in it.

And about the details of files....Actually they are customed most by themers.Even a theme that only includes metric.ini in it can be a new theme(XD).So there isn't any instruction about them.

Emm, yaa, maybe it's called opening movie
No, i have search in any folder, but i can't found anything like video or picture like their opening movie, so i really confused about it, how it can be play but nothing can found in it source folder?:S

I think maybe it isn't just a theme, maybe they made a change in the application :S
Because it must be installed before, and in the folder, they have 1 stepmania.exe file to play, so does'nt like another theme that just copy and paste it to folder in stepmania folder itself to change the theme, but installed like new application.

Or it might be a ActorFrame look likes movie.There are many ways to make it,but needs some theming tech.

Be Installed?well that should be the problem.If the opening movies were in the main program,it's out of theming area often.QAQ,the only way to find out is edit the main program,and I know nothing about this.