To delete an Important Date, click on the Important Dates link on the left hand navigation. Next, locate the date you want to delete on the table and click the corresponding pencil icon in the far right column. (Note that Upcoming Dates are listed under one tab, All Dates are listed under another.)
Click on the Delete button at the bottom of the page.
Please keep in mind that this only applies for Important Dates that you have created directly. Any date automatically created when you entered a round, such as a note maturity, warrants expiration, or options void date, will need to be deleted by editing the round.