Install WordPress at existing site, need to delete files?

Total novice here- I managed to upload a place-holder home page (and only that) using some freebie web publishing app, now I’ve decided to use WordPress using the one-click custom installation to put a blog there temporarily until I get a real website going. The wordPress install box asks for my domain but says “Please be sure there are no files there now”. Does this mean that I have to delete the home page I uploaded first? How do I do that? (I no longer have the web publishing app I used, I have Dreamweaver but can’t figure out how to use it).
Also, when I’m ready to publish a designed website to replace the Wordpress blog at the same site, will there be any problem making the switch that I should be aware of?