Do not understand what you mean, first part it seems like you are saying can install (without uninstalling old whatsapp first) so it will update the existing app to the version installed, second part it seems like you are saying I need to uninstall the older APK first then can install a new whatsapp apk
Q1. "Usually a newer version will update the existing app nothing further to be done" > I have whatsapp apk installed already and did not uninstall it, if I install the newest whatsapp apk, will I need to do the activate whatsapp (input sms code) and restore whatsapp backup again?
Q2. "if your using older APK u need to uninstall the current one for it to install" > I have whatsapp apk installed already and now I uninstall it, then I install the newest whatsapp apk, will I need to do the activate whatsapp (input sms code) and restore whatsapp backup again?