If you use an Android Phone you most likely get your apps from Google Play Store, but updates can take lots of time and data if you have lots of apps. But earlier at Google I/O, Google talked about the new update system that would only download the parts of your apps that changed along with encrypting them so paid apps couldn’t be ripped off.
Reports now show that system has been started and will work even on older phones (2.3, 4.0 …) and can save you lots of data when updating apps. When you update an app it will download the part you need then start installing it if that’s all you need before the full download is done. This update should happen the next time you load the Google Play store on your device and happen without you having to do anything because the Play Store updates its self all the time.