I created a test website of our existing live website for trying the installation of a new skin.For this created a copy of the website folder in d drive.Using this d drive folder created a new website in iis with a new port number with domain name same as the existing site name.Everything is working fine.But the only issue is that in the new website host-host settings -physical path is of the live website's.it is not showing the d drive path of the new folder created for this test website.How to change this?Without changing this,if proceeded with skin installations it will get installed in c drive path which is of the live website's.That may affect the live website no?How to solve this?

The question isn't clear to me.

You made a copy of your site, but you are using the same domain name, but bound to a different port?

I'm not sure that this will work. I would use a somewhat different domain name, and add that in the portal alias table of your DNN site. You could use the same or a different port depending on your choice/