Yes, you can change the style of your blog comments by making edits to the CSS file applying to your blog in the template builder.
The following class names may prove useful when selecting which elements you would like to customize:
|.comments-listing||listing of all comments|
|.comment||author, comment, and date (all)|
|.comment-from||comment author name|
|.comment-body||the actual comment|
|.comment-date||the comment's date|