Remodeling my Site, Time for a Change, But...

So the site is up and functioning and getting decent traffic. I want to make it more appealing and engaging. I just don't want to Farg things up and have a site "In The Works" for the world to see. I want to Remodel, New Theme, Positions, Layout, Blog etc, in a separate directory, add-on domain, sub-domain, wherever. What do most people do? One of those or Something Completely Different? I have a couple of domains that are dormant at the moment so I could park it on one of them. Just don't want to screw up my ranking and such.

Just wanting some input as I'm sure there are a few possibilities and everyone has it's bennies.

Looking forward to hear what y'all have to say.

JJ

Make a local backup of your site and install it on xampp or wamp, or a similar program. Developing is faster when you don't have to upload the file in between changes.