Unable to install iOS 18 in my iPhone 15 Pro Max

So me and my dad upgraded our phones to the IPhone 15 Pro Max earlier today, and during set up, we have had to download the IOS18 update. That started at around 11:30. It finished downloading for me at like 3pm, since then it’s just been circling after pressing install. Is there any help I could get or am I just going to have to let it take its sweet time? Thank you

[Re-Titled by Moderator]