In case of windows phone 7 all the system software updates will be pushed to the device, When a software update for your phone is available, you’ll get a notification.
If you’re curious about whether your phone has found an update, you can do the following.
1. On Start, flick left to the App list and tap Settings. Then tap Phone update
Note: You can customize the notification settings and connectivity methods your phone uses to check for updates. By default, your phone uses your cellular data connection to check for updates and notifies you when an update is found.
2. If an update is available, and you want to learn more and install it on your phone, connect your phone to your computer using the USB cable that came with your phone.
3. On your computer, run the Zune software if it doesn’t start automatically, and then, in the Zune software, select Settings > Phone > Update.
Note: If your computer doesn’t have the Zune software installed, you’ll be prompted to download and install it before you can update your phone. The Zune software will provide an estimate of the time required for the update to complete.