iPhone 6s unable to install update

so I have a 6s currently version iOS 11.3 I am trying to install 13.3. Every time I try, it downloads but I always get an error message saying “an error occurred installing iOS 13”. I have enough storage, I’ve restarted my phone, I have also deleted the iOS download and redownloaded it but I always get that error message. Please help! I can’t update some of my apps because of it and some I pay bills on.