why wont my iphone 7 update to iOS 15.71

so i deleted basically everything on my phone but it keeps saying

”Unable to Install Update

An error occurred installing iOS 15.71.

Retry

Remind Me Later”

i rlly dont know what i did wrong, i have enough storage and it is downloaded, just not updated. i cant download anything else now cuz the update is downloaded and sitting in my storage, taking up all of it. i have 1gb left, idk what now.