When you get the error “Unable to connect to web server ‘IIS Express’ you probably try to start the website with a port that is in an excluded port range

List the excluded port ranges with the command below:

netsh interface ipv4 show excludedportrange protocol=tcp

Sample output may look something like this:

Now to change the port for your web site right select the dropdown right to the IIS Express label

Then select [YOUR PROJECT] debug properties and change the port on the properties page (highlighted below)