Imported plan

I know this question has probably been asked and ansered before, but here goes anyway.  I imported the 20 week Oly (2x) plan.  However, I later learned the date of my first race and wanted to adjust the plan to end just prior to the race.  I tried to delete the plan and import it again.  Can anyone tell me how to successfully change the start and end date to fall in line with my race?  Thanks