Death of Web Master

My sympathies for your loss as well. 

1. DW 4 is unfit for modern use.  It's an outdated relic from another era. 

2. It's a damned shame this project wasn't moved to an online CMS like open source WordPress -- https://wordpress.org/ It would have made your job 100% simpler.

3. If you know the hosting server's log-in credentials and password, you can use free FileZilla FTP client to download files from the server to your local computer hard drive.   To install FileZilla, click the green download button at the link below.

https://filezilla-project.org/download.php?type=client

4. Use any modern code editor to make site changes.  Below are a list of free and paid ones. 

-- Adobe Dreamweaver CC - https://www.adobe.com/products/dreamweaver.html
-- Codespaces (free, browser-based) - https://github.com/features/codespaces
-- Nova (Mac only, formerly called Coda) - https://nova.app/
-- Pinegrow - https://pinegrow.com/
-- Sublime Text - http://www.sublimetext.com/
-- Visual Studio Code (free) - https://code.visualstudio.com/

This should buy you some time until you can have the site rebuilt on a more suitable platform for your needs. 

Best of luck. 

First of all, my condolences for your colleague.

When DW opens, all you have to do is modify the documents and content you want, and then once they've been saved, simply place them online (CTRL+SHIFT+U).

Sorry for your loss. I'm not entirely sure I understand your issue. Dreamweaver 4 is very old, over 20 years. That login could be for an Adobe account ( https://account.adobe.com/ ) or it could FTP information to connect to your remote server where the website is hosted.

If the program opens you should see a files panel (Window --> Files if you don't see it anywhere) and then you can edit your site. However, depending on your level of expertise, it may be worth just looking to hire an outside contractor to either 1. make some updates for you until you have the expertise in-house, or 2. be able to be shared private information such as logins/etc. to help your team understand what is setup and how to make edits yourself for the time being.