How large will an IPhone patch be?

I am working on an IPhone game. Currently the .ipa file is about 250MB. When I open that (in WinRAR) I see that the exe is about 65MB and the rest is made up of various resources.

When I publish this to the app store I assume the download will be 250MB.

If I then create a new version that has just (say) changed one of the assets then this new .ipa file will also be about 250MB. If I upload this new version to the app store will the users have to download the whole 250MB again or will they just be able to download a small patch that contains the changed asset?

Many thanks

Use asset bundles, so the game can fetch the updates from your server.

We are currently considering our options, so it would be really useful to know how the store behaves. Can we create small patches for the app store or will every update cause a download of the whole game?