Apple iOS 8 is here. If you are eager to try it out, you can download it over the air by checking updates on your iPad or iPhone. The problem is the update is requires 5.7GB of space. Unless you don’t have any pictures, videos and apps on your iPhone, i doubt you will ever want to update it over the air.
So, the best and most reliable way is still to connect your device to PC or MAC, do a backup of everything and select “check for update” when the prompt pops up on iTunes — not “restore iPhone.” The latter option will indeed wipe all content from your device.
Enjoy your new iOS 8.