Apple recently released its latest operating system, iOS9, which is compatible with almost all iPhones and iPads. Apple has claimed that although designed for the latest equipment, the upgrade will improve the performance of older devices too.

Owners of an old iPhone 4 or even an original iPad, will not be able to join the party though as these devices are not compatible with iOS9. For those that have still not downloaded the upgrade, we recommend a good clear out of all the old apps no longer used, as well as archiving all the photos and videos not needed on a regular basis

By cleaning devices of old files, users should be able to avoid the problems of previous years, when users complained there was not enough room on their devices to apply the updated operating system. Perhaps in response to previous size issues, Apple has reduced the size of iOS9, only around 1.5GB, compared to previous incarnations.

To see if you have room for the upgrade, click through Settings > General > Usage and see what you have left. Although you might have the room, before you commit to the upgrade, be aware things can go wrong and it’s a good idea to back-up your device to either your computer or your iCloud.

Of course, it wouldn’t be Apple it there wasn’t something to upset adoring fans. The issue this time is iOS9 Wi-Fi Assist, which risks eating up the data allowance of users, without them knowing it.

Although there are a host of exciting new features with iOS9, including better battery life, improved apps and an even smarter Siri, Wi-Fi Assist might give users a shock next time their phone bill arrives. The idea behind this little feature is that it will automatically switch from wireless networks to 4G data when it detects Wi-Fi running too slowly.

The problem is that in doing so, the phone might switch from your local Wi-Fi, at home or in the office, to your bundled data usage without you noticing the change. For iPhone users with limited data contracts and a penchant for films and live streaming, it could prove costly.

Apple thought they were being helpful, but for those who don’t want to take the risk, it’s easy enough to turn off. Enter the settings menu and click on Mobile Data, then scroll to the Wi-Fi Assist toggle switch and turn it off – the toggle switch should now be white, not green.

A simple solution to what could be an expensive helping hand from Apple.