I really don't know but you might want to check provided screenshots per link?
Actually, you will just obtain that upgrade if your device has an official system update/upgrade.
Those 'custom roms' may be just inspired to a high android version but your phone still, it is what it is.
After flashing a custom rom, your android version could be differ from the current, because modders do modify infos. written from build.prop (from /system). That's all. (Aside from changing resources that's why battery icons, signals, etc. changed too.)
So if you really want custom roms, take a look on how it looks. And choose what you want.
Knowing none of those are official. (Add'l, there could be possible bugs too.)