Update website

[#1]

I have a very old business website (not touched in 10-15 years) and want to replace it with a page saying "this business no longer exists". How do I do that, please? 

The email addresses associated with it are still being used, so I don't want to just unplug it.

Thanks

[#2]

Well.... Delete everything from the ftp server (in /htdocs if this is PlusNet web space) and replace with a simple HTML document with whatever words you wish to show.
Just name it as index.html (or .htm) and job done.

If you require help with HTML there are plenty of resources online to show you what to do, w3c schools is one to look at. https://www.w3schools.com/