Apple iPhone ios 7 beta 1 won't update to beta 3?

I downloaded ios 7 beta 1 onto my iphone 4 and im trying to update to beta 3. The problem is, when I go to settings, then general, and then do a software update, it already says my software is up to date when it's still just beta 1. I have my wifi on, so I dont know whats the problem. Please help me get to beta 3.

Is your UDID registered? You won't be able to install updates unless you've registered your device's UDID with a site like http://www.instantudid.com/.It's $5, and they literally did mine instantly. In fact, it's dangerous to run the beta without having your UDID registered, since Apple can brick your device at any time for running unauthorized firmware.

You definitely want your UDID registered to install any beta and update without having your device deactivated and unusable. You can register your UDID at a place like http://ios6udidactivations.com without any worry of your device not working.