6. Once you’ve installed the profile, you’ll be asked to reboot. On doing so, go to Settings > General > Software Update and you’ll see the current beta available for download. This is it: your last chance to back out.
7. Ensure your device is connected to a power source. Tap Download and Install, Agree, and – once the whopping installer’s downloaded – Install Now. Depending on your Wi-Fi speed and how many lucky stars are stashed about your person, you should be rocking iOS 12 within half an hour or so.
If you decide you’ve made a terrible error at some point, plug your device into iTunes and restore from the back-up you took, although be mindful any non-cloud data added to your device since that point will be lost forever.
Alternatively, if you’re happy with the beta, but want to get off the pre-release software train when the final version of iOS 12 yomps on in, you can do so. Install the final release of iOS 12 (before the next set of betas starts), then go to Settings > General > Profile, tap the installed profile and then tap Remove Profile.