How to swap UI of a custom rom with other rom?
If your ROM has Theme Chooser integrated into the system, I would recommend just switching to an AOSP theme, like this KitKat theme.
You can check if you have Theme Chooser by doing any of the below:

Android 2.3: Check if there is an app in your launcher named 'Theme Chooser', with an icon of the Android robot colored four different colors
Android 4.0+: Check if there is any theme-related menus in Settings.

If your ROM does not have Theme Chooser, then you would have to get your hands dirty with manually themeing system APKs. Go to xda-developers for more info and tutorials on that.