CIS and Comodo firewall are free.
As Melih said, the website has not been updated yet, and the current (outdated) download page is very confusing and may seem like you have to pay (but it is free).
The direct download for the installer of free CIS 2025 (and firewall) is here.
For now, the updater within CIS will not update from the old CIS to CIS 2025.
Updates through the program will be implemented reasonably soon.
If you would like to update to CIS 2025 now, then it is probably best to do a clean install:
- Export your CIS configuration if you want to use it in CIS 2025.
- Uninstall the old version of CIS.
- Run the CIS cleanup tool to delete any CIS remnants (get the latest version here) - sometimes the links in the post won’t open. If that is the case, copy the link, open a new browser tab, paste the link into the address bar of your browser, and press return…the cleanup tool should download.
- Install CIS 2025 (the direct download is here)
- Import your configuration settings if you want.
- If desired, go into the firewall tasks, select “stealth ports”, and select “block incoming connections” (since this is not done automatically).