I want to delete all existing files as they are stopping me from furthering on in my quest for other sites?
This doesn't sound like it's related to the HTML5 Pack. I don't think that you need to delete any files. Try opening the Files Panel (Window > Files) and use the drop-down control at the very top to switch to another DW Site.
Use Site > Manage Sites to define a new Site in DW. The Site selected inthe list when you click "Done" will become the selected Site.
Hope the helps,