will I have top update my software again if I erase all content and settings

will I have to update my software again to the most up to date version like I did the first time if I erase all content and settings. I want to restore the phone to the backup from a different device you see which was the most recent one. The problem is it was iphone 8 and now this one is iphone7 so not sure if this is possible even though I have now updated the software to most recent version