With WebDwarf, you can create only one page per project. So when you publish a project, one html page is produced and the ims file is copied to the site as a backup. (If you use SVG mode then an SVG page is produced instead of the html)
The ims file will have then name you used when use saved the project (the default is 'unnamed.ims')
The html file has the name given to the page in the page name box (in the toolbar next to the page background button). The default name is 'index'. If you want your page to have a different name, just type over the word 'index' with your new page name.
If you want a different name to appear as the 'Title' in your browser's caption bar, just edit the 'Page Title' in the 'Page Editor'. The Title will not affect the name of the html file created.