Changes to websites

I need some help to make some small changes to my websites:

I would like to change the domain name for https://optical-network-certification.training/ to a subdomain of the main website, https://fiberguide.net. The new domain will be https://optical-network-certification.fiberguide.net

This means that you will have to create a new subdomain in fiberguide.net. You will also have to redirect any traffic to https://optical-network-certification.training/ to the new subdomain. In addition, all pages on the site should be forwarded to the corresponding sites on the subdomain.

Make some changes to fiberguide.net main page. The sliding banner banners on the page our site replace that banner with a static and easy to load banner. In bold clean white text (like one on the optical-network site) include the text “FiberGuide optical network training and consulting”.

Replace the image labeled “Wide Area Network Solutions” and replace it with a suitable image labeled (Optical network consulting) - pointing to https://fiberguide.net/wan-networking/optical-communication-consulting/. Replace the image labeled “FiberGuide Network Engineering Services) with a suitable one labeled “Connectivity Sourcing” - should point to https://fiberguide.net/wan-procurement/

Include a clickable phone number in the headers of both the main site and sub-site.
Any other suggestions you might have.

Important: In your response, please let me know what precautions you will take to not bring down the website. Last time we attempted we lost the site for a whole and we had to pause the project.