How to put iphone update on other iphone from itunes?

I downloaded and installed a software update on itunes for one of my iphones. How to I get the update on my other iphone? I have plugged my iphone in and can see the download in my downloads but I don't know how to put it on my phone? Everytime I click update it tries to download the update again.

Is it the same model phone? If not it won't work and you will have to redownload it. If it is locate where the file was downloaded to and the go back to iTunes on the 'update' or 'restore' button hold down the control button and click update or restore at the same time, find the file and select it should work