"Slide to Upgrade" STUCK

I just tried updating my iPhone 4 (incidentally I was also in the process of transferring data over from an old phone) and the new version won't let me complete the install. After it asks me to select a network and trust my computer, it asks me to "Slide to Upgrade" but won't let me swipe.

Another discussion about this going on here: My iPhone is coming up with 'slide to upgrade' but won't let me. Is this meant to happen? - iPhone, iPad, iPod Forums at iMore.com.

Anyone else having this problem? Rebooting isn't helping.

I don't know if you're referring to the upgrade that came out today (iOS 9), but the iPhone 4 is not qualified to receive it, which makes it a nonissue.

The latest iOS for iPhone 4 is iOS 7.1.2. The iPhone 4s on the other hand can supposedly run iOS 8 and 9 but i wouldn't suggest it because the processor is in my mind inadequate to run iOS 8 successfully much less iOS 9.
Your only real option now is to connect your iPhone to your computer via USB, open iTunes and restore the phone to factory settings, that will load the most recent version that the iPhone 4 can run. Once that is done restore the phone from your most recent backup. You do have backups I assume?
In addition I don't understand how you managed to download the iOS upgrade in the first place. If you attempted to upgrade via Software Update it should have told you that your iPhone 4 does not support that iOS.