Apple will release iOS 9 on September 16, which means that you have a few days to get your hardware ready for the upgrade.
Here's what you need to do to make sure that things go smoothly for you.
Will you get iOS 9?
First things first - will you get iOS 9?
Here is a complete list of the devices that are supported by iOS 9:
To know what device you have, use this page to decipher the model number which you can find on the back of the device or under Settings > General > About > Model.
Backup your data
Before you do anything major such as upgrading your device you need to make sure that you have a backup just in case things don't go smoothly. You can either back up your data to iCloud, or if you don't have enough space you can take the old-school road and connect your iPhone or iPad to a PC and do the backup through iTunes.
Details on how to carry out a backup can be found here.
Spring clean your device
Chances are good that your iPhone or iPad has accumulated a lot of detritus over the months and years, so what better time to get rid of it than now. While iOS 9 doesn't need as much free space to install as earlier releases, getting rid of apps that you no longer use -- or perhaps have never used -- makes good sense.
Update your apps
If you've not updated your apps in a while then this is a good time to do so because a lot of the apps will have been updated to make them compatible with iOS 9.
Find the App Store app, tap on it and then click on Update. Once in there you can kick off the update process.
Put your photos in the cloud
Another thing you can do is to upload your photos to the cloud. CNET has an excellent rundown of some of the free services that you can use for this. Know your passwords. Following the upgrade you'll need to enter your iCloud password in order to be able to reconnect to all your data and photos. If you don't have this close to hand -- remember, having it on the device you're upgrading isn't all that convenient -- then this might be a good time to do that.
Also, if your iTunes backup is encrypted, then remember that you'll need that password if something goes wrong!