How do you update your iPhone without having it delete everything?

You can't upgrade your iOS on your iphone without loosing some of your jailbreak. There are some feature (like battery percentage) that are farther in the software and will stay, but Cydia along with most (if not all) of your jailbreak apps will be taken off. You can backup your apps using RockApp, but you loose your data within that app. If/when you update your iphone you can jailbreak it with RedSn0w then download RockApp again from Cydia and get your apps back, but you may just want to hold off on updating and just stick with what you have.