Unable to update iPhone to v5.1?

Try later.

This has solved loads of people who have this issue and have used an alternate DNS setting. Below are instructions for both iPhone OTA and on you Mac

If you are getting the error message "Unable to check for update" when you try an OTA (over the air update)

Change DNS Servers

Settings -> Wi-Fi

Click the blue arrow on your connected network

Delete everything in DNS and replace it with 208.67.222.222, 208.67.220.220

Try again

If this works, you will probably want to remove the WiFi network using "Forget This Network" and then reconnect to it to get your original DNS servers back. Alternatively, make a note of the original DNS servers before deleting them and replace it after you are done.

If you are getting the error message "Unable to check for update" when you try through iTunes

On your Mac

Choose Apple menu > System Preferences, and then click Network.

Select the network connection service you want to use (such as Wi-Fi or Ethernet, unless you named it something else) from the list, and then click Advanced.

Click DNS, and then click Add ➕ at the bottom of the DNS Servers list. Enter the IPv4 address for the DNS server.

You can use OpenDNS

208.67.222.222

208.67.220.220

or

You can Google Public DNS if you want

8.8.8.8

8.8.4.4

My iPhone is unable To complete the download v5.1, through the settings option, the message shows "could not update, an error happened".

March 7 @ 2pm updated my iPad 2 at doccters office no problem

Got home got error on iPhone 4s and apple tv. Tried everything from rebooting to 8.8.8.8 and 208.67.222.222

Nothing worked on iPhone 4s even went back to doccters office but no go.

On apple tv at home I changed to 8.8.8.8 and it worked just fine. But iPhone 4s it didn't

I restarted phone tried different wifi networks

Finally this morning I got it to work!!!!

Ok not sure if this matters but still has open dns entered 208.67.222.222, 208.67.220.220

But I did that other reset hold down home button and power button until it turns off

Then I turned it back on went into software update and it started updating.

Well it worked for me and haven't read this solution yet.

Good luck

Tried everything to update to ios 5.1. The software downloaded, and when I click "Install Now", it "verifies download", then I get an "Unable to Install Update" and that "An error occurred installing iOS 5.1". The dialogue box gives me options for either "close" or "settings". I've restarted the iphone to no help. The software was downloaded directly to the phone via wifi network.