how to delete files in macOS automator

Good luck with this. Automator is great with single-threaded, single-path solutions, but is overly cumbersome when it comes to any kind of logic processing (such as determining which document is front most).

To address your question directly:

> I am just trying to delete a specific file from a specific folder but I can't work out what actions I need to do this. I've practically sorted out everything else.

Since you know the path to the file, you can combine a 'Get Specified Finder Items' to locate the earlier file, then add a 'Move Finder Items to Trash' to discard it.

However, my thought is you're doing this the wrong way. Any script that demands a fixed filename in a specific location is bound to break at some point (as well as being inflexible to change).

While it might take a little more work (and learning curve), this task sounds far better suited to AppleScript than Automator. The big advantage is that AppleScript is far more flexible and actually understand things like variables, so you can target items indirectly (e.g. the front document in any application, regardless of what it's called, and even without that application needing to be frontmost).

For comparison, here's an AppleScript that will delete a specific file from your Documents folder

tell application "Finder"
	delete file "Old File.txt" of (path to documents folder)
end tell

To be fair, you can take small-steps using the Run AppleScript action within your Automator workflow before migrating to Script Editor itself.