I'm not sure what you're getting at. Register and log in to what? The apps? No, you don't have to log into the apps. But you can only disable the apps that came with the phone (system apps). Anything that you installed you can just uninstall.
To disable an app that came with the phone, perform these steps:
- Pull down the notification bar and locate the little gear/sprocket icon in the top right corner. Tap it. The settings will open.
- Scroll down until you see Application Manager. Tap it. The application settings will open. Notice that at the top of the screen, there are three tabs: Downloaded, Running, and All. Tap All to view all the apps on the phone.
- Scroll down until you find a system app that you want to disable (like S-Voice, S-Memo, AT&T Navigator, etc.). Tap the name of the app and a settings window for that app will open.
- At the top of the settings page, you will see the name of the app and its icon. Immediately under that will be two buttons: Force Stop and Disable. If the app has been updated at all, the second button will instead be Uninstall Updates. If it says Disable, tap it to disable it. If the button is labeled Uninstall Updates, then tap it and uninstall the updates. After the app reverts, that second button should now be labeled Disable. Tap it to disable the app.
For apps that you have installed, you can use this same method to uninstall them. Open the settings for the specific app and tap the Uninstall button.
Hope that clears things up.
Oh, and a word of warning: if you don't know what something is...DON'T disable or uninstall it.