Why can't I update to ios 7 on my iPhone 4?

I have the iPhone 4 and it says that's there's no new updates and it 3:05 pm

Are you connected to Wi-Fi? That might be the problem

The schedule for the update is users on the US east coast around 1 PM and west coast around 10 AM, while Europeans will get it sometime in the early evening hours and Asia during the night. So depending on your region, the update will be available for your device. You can even refer a post on how to update to iOS7 which i have given in the source link. That post shows how to update through over the air and updating using the iTunes(from PC).

Wi-fi or itunes. If you do it on a computer make sure that your iTunes is fully up to date since they released a new version of iTunes today as well.

Also there are tens of millions trying to update all at once.expect delays.