How to upgrade Laravel 8 to 9

Updating Dependencies

PHP => 8.0

Composer Dependencies

PHP=> “^8.0”
laravel/framework => “^9.0”
facade/ignition to replace “spatie/laravel-ignition”: “^1.0”
nunomaduro/collision => “^6.1”

Lastly need to change

Trusted Proxies File

app/Http/Middleware/TrustProxies.php

Laravel doc check more TrustProxies

And update your composer

More details laravel Upgrade Guide