Today’s the day: iOS 9 makes its debut, and maybe you’re one of the many users who are excited to upgrade your iOS device. I’ll cover how to upgrade to iOS 9 and how to do a fresh install of iOS 9 in this article. (If you’re wondering if you should upgrade in the first place, we think you should.)

But then, if, for whatever reason, you decide you need to downgrade back to iOS 8, I’ll also show you how it’s done. Keep this in mind: The window to revert back is small. Apple will eventually stop authorizing iOS 8, and when that happens and you have iOS 9 installed, there’s no going back.

If you’re very concerned about your apps not working or your device not performing up to par, don’t upgrade to iOS 9 immediately. You’d be better off waiting for Apple to release the first major update to iOS 9, which may address some of the bugs you are afraid of running into, and it also gives developers time to update their apps.

Is your device compatible?

Apple says that iOS 9 is compatible with the following devices:

iPhone

• iPhone 4s
• iPhone 5, iPhone 5c, iPhone 5s
• iPhone 6, iPhone 6 Plus, iPhone 6s, iPhone 6s Plus

iPad

• iPad 2, iPad third generation, iPad fourth generation
• iPad Air, iPad Air 2
• iPad Pro
• iPad mini, iPad mini 2, iPad mini 3, iPad mini 4

iPod touch

• iPod touch fifth generation, iPod touch sixth generation

Some features in iOS 9 may not work on older devices in the list above. If you’re an owner of a device that’s on the older side of the compatibility list, consider putting off the upgrade to iOS 9 until you get more information on how the new iOS performs on your device.

Back that device up

Before you upgrade to iOS 9 (and, when iOS 9 is installed, before you install any iOS updates), you need to back up the data on your device. You can back up via iTunes on your Mac (fastest) or back up to iCloud (more convenient).

We have complete instructions on how to back up your iOS device in iTunes 12 or via iCloud. (The linked article is about preparing for iOS 9, but it includes backup instructions.)

Upgrade to iOS 9

OK, it’s time to install the new iOS. You have two ways to install iOS 9: Directly on your device using a wireless connection, or through iTunes with your device connected to your Mac. If you want to install directly, you need several free gigabytes of storage space available. If you don’ have to room, use iTunes on your Mac.

Install iOS 9 directly

1. Make sure you have a good amount of battery life left. Anything above 60 percent should be fine, but the weaker your wireless connection, the more taxing the connection will be on your battery. Plug in your device, if needed.
2. Tap the Settings app on your iOS device.
3. Tap General.
4. You’ll probably see that Software Update has a badge. Tap Software Update. If it doesn’t have a badge, tap it anyway; this will trigger the phone to check to see if an update is available.
5. A screen appears, telling you that iOS 9 is available to install. Tap the Install button. The download and installation will take a few minutes.

Install iOS 9 though iTunes on your Mac

1. Connect your iOS device to your Mac using the sync cable and then launch iTunes.
2. If iTunes already knows that the update is available, an alert will pop up, asking if you want to update your device. Click the Download and Update button to install iOS 9 right away. If you want to download the update but install it later, click Download.

If you don’t see an alert, click on the device icon in the upper left and then click on the Summary tab in the left column. In the right window, click on the Check for Update button. If it’s available, the version of iOS 9 for your device will download to your computer for installation.