upgrading IOS 17.7 to IOS 18
can i upgrade With iTunes without backup?
iPhone 15 Pro Max, iOS 17
Update software on iPhone, iPad, or iPod touch in iTunes on PC - Apple Support
Iit's a risky thing to do to upgrade your iPhone without making a backup. There's always a chance that something will go wrong, and such a failure would require you to restore your iPhone to factory settings, then without a backup all your data will be lost.
Regards.