Delinking Dreamweaver

I’m trying to redo with WordPress a site that’s already online (with Dreamweaver). I’m hoping for something cleaner, easier and friendlier to make updating more amenable. The problem is with the WordPress files I’ve downloaded, anything I try to open starts up with Dreamweaver. Is there a way around this? (I’d like to be able to play around with a theme to design the site on my iMac (running OSX 10.3.9) and then upload/replace the current Dreamweaver-written site in one fell swoop…any help would be appreciated.