You can basically change the title for every page.
For default.aspx and archive.aspx, search inside the code behind files for these pages -- default.aspx.cs and archive.aspx.cs. You'll find in there
Page.Title = ..... You can change it to what you'd like. The default.aspx.cs actually has "Page.Title =..." in there several times depending on what type of posts are being displayed.
You can also change the title for your pages. In the page.aspx.cs file, in AddMetaTags(), the title is being set:
base.Title = Server.HtmlEncode(Page.Title);
You can change that to something different ....
base.Title = "some other title";