CodeIgniter 4 can be installed using three ways –
Manual Installation –
You can download the latest release of CI 4 from its official site and can place it in your server root directory after extracting it.
Using Composer-
You can install it using Composer. For installation using Composer, you have to run a command
composer create-project codeigniter4/appstarter project-root
but for this first, you need to download and install composer so you can download composer from this link
https://getcomposer.org/
Using GIT Repository –
You can also get CodeIgniter file from a git repository of CI 4 you can use the below link to get it and after download, you can put it in your root directory.
https://github.com/bcit-ci/CodeIgniter