uninstalling WhatsApp
You can't remove pre-installed apps without root access. These system apps are stored on the system partition, which is generally mounted as read-only and prevents non-root users from modifying it.

However, the system partition is also usually separate from the user partition where you install apps. That is, the system apps by themselves don't take up any usable space. As long as you clear data (instead of just clear cache), you can disable the app and it won't take up any usable space.