I needed to go back to iOS 7 after a few apps, most notably Whatsapp, no longer worked properly. I also had no restore points for some reason.

Here’s a way to turn your iOS 8 iPhone back into an iOS 7 iPhone:

1. Attach phone to Mac
2. Start iTunes
3. Hold Power and Home Button on the phone. When it restarts let go of the power button and only keep the Home button pressed.
4. iTunes will say it detected a phone in recovery-mode
5. Proceed with the recovery instructions.

You don’t need to donwload any images before hand, iTunes will do it for you.

In my case I ended up with a completely blank iPhone. But I could restore Contacts, some settings etc. from iCloud.