To convert your CentOS8 operating system to AlmaLinux do the following:

-Make a backup of the system.
-Disable Secure Boot because AlmaLinux doesn’t support it yet.
-Download the almalinux-deploy.sh script: run the system update and upgrade command

In CentOS and run the system update and upgrade command.

# sudo dnf update 
# sudo dnf upgrade

Install Curl, if you don’t have it:

# sudo dnf install curl

Download the CentOS 8 to AlmaLinux migration script.

# curl -O https://raw.githubusercontent.com/AlmaLinux/almalinux-deploy/master/almalinux-deploy.sh

Run the downloaded script with sudo rights or as root. Thiswill download all the necessary packages and replace the default CentOS repos, logos, and other things with AlmaLinux.

# sudo bash almalinux-deploy.sh

Check release info

# cat /etc/redhat-release 
AlmaLinux release 8.3 (Purple Manul)

Check the default kernel by running:

# sudo grubby --info DEFAULT | grep AlmaLinux

Output:

title="AlmaLinux (4.18.0-240.15.1.el8_3.x86_64) 8.3 (Purple Manul)"