Cannot use port 80 for my application

Question

I have an application called NTWebService, and this uses port 80 to listen to my computer. However, When I run the application, I get an error:

Listen failed.

More exactly,

Initializing sockets...
Sockets Initialized OK
Starting Listen thread.
Starting Threads
.....CS:Listen: bind failed: 10013
Listen Failed

is shown on the window that opens when I run the application.

When I typed netstat -nao on command prompt, I found that a process with PID 4 is using port 80, and that that process is System and I cannot delete it. When I did some research, most of them had said

1. On Control Panel, open Programs and Features
2. Click on Turn Windows features on or off on the left pane
3. Locate Internet Information Services
4. Uncheck the textbox for World Wide Web Services

However, when I checked this, it had been unchecked. I basically had nothing to do on it. I also tried another way:

1. Click on Start button and right click on Computer
2. Click Manage to open Computer Management
3. Click on Services and Applications from left pane and double-click Services
4. Locate World Wide Web Publishing and turn it off

However, I don't even see World Wide Web Publishing on the list, so again, I could not do anything about this. I also don't think I can tell NTWebService to change the port it listens on. Is there any other good way for this application to listen on port 80?