There is no such thing as a iOS theme unless you've jailbroken the iPad. If you have jailbroken the iPad, then themes and how to install/apply them will be specific to the theme app you've chosen. Hold in mind that many jailbreak apps are not yet iOS 9 compatible. And that about limits what I know about jailbreak theming.
If you are talking about something else, please provide more details.
Thanks for instant reply, yes my iPad Air 2 is jailbreaked already
Just in case there is a theme that fits on iOS 9 please educate me
On how to install/apply my desired theme
I would expect a theme app to have instructions on how to download and apply themes. Downloading the themes by themselves would be pointless. You need the app first. Android themes work much the same. You need an app, then you download the compatible themes.
So, look for a theme app that is compatible with iOS 9. Read whatever instructions are in that app (or in the app's description), and download the themes that go with it.
Of course I could be completely wrong. Hopefully someone with more knowledge on the subject will wander by and give you more detailed instructions.
I'm going to assume that (1) you've gotten the theme from Cydia and (2) the tweak called "Winterboard" was also downloaded (generally, you need Winterboard to run themes on a jailbroken device).
The biggest issue right now is that Winterboard has not been updated to run on iOS 9. So, it most likely is the reason why you are have issues with it. So, really, the only thing I know of to do is wait until the developer of Cydia (saurik) updates it.