Attempting to update app asks for a different iTunes account password I am trying to update WhatsApp. It is asking me for an iTunes password of a different email address and I can't change it.

I rebooted my phone, signed in and out of iTunes and it is not changing it.
What should I do?

Will I lose the existing conversations if I change the Apple ID following the instructions in the answer provided (I.e. Deleting whatsapp in the old ID and downloading it with the new Apple ID? Or is the conversation linked to the phone number, not the app?
The Apple ID being requested will be the Apple ID that was used to purchase the app originally. It can't be changed, since it is linked to the specific app. If you wish to use your Apple ID instead, you can delete the app from the device and re-purchase it in the App Store using the correct Apple ID.