iPad will NOT update

I am having issues gettting my iPad to update. I transferred all of my purchases so that I could start downloading the updates. iTunes downloads the entire update, which takes about 50 minutes each time (I've done this about 3 times now) and as soon as it is done downloading, I get an error message that says the session has timed out and cannot download, telling me to try later. Is there something I am doing wrong? My internet connection is extremely fast and never cuts out while I am waiting, nor does my computer shut off at any time since I usually sit here and do other things while waiting... please help!