Automatically update all Apps
Go to Google Play --> Menu --> My Apps --> Update All

The "update all" should be near the top right corner. The default for most apps is "allow automatic updating". This can be changed for each app from this same screen by clicking on the app and checking the box "allow automatic updating".

BTW sometimes an app requires a manual update. The update all function will leave those out you have to click on each app and hit the UPDATE button.

I do know Google Play will not let you update an app if it thinks the update is not compatible with your version of software or hardware.