If you have a standard retail Xbox 360, there is no hidden "secret button" to unlock a full file manager. Any website claiming otherwise is likely a scam or spreading misinformation.
For advanced users who need true file system access (to transfer game mods, extract save files, or back up profiles), Microsoft provided a tool called as part of the Xbox Development Kit (XDK) . This method requires: como entrar al gestor de archivos en xbox 360