Hello Priyanka, and welcome to planDisney!
With your visit to Walt Disney World Resort coming up in just a few days, I'm sure you want to make sure all your plans are in place for your magical vacation.
If you would like to change your 
Disney Park Pass reservations to a different park, you'll need to first cancel the reservation you currently hold, and then make a new Disney Park Pass reservation.  Before canceling, check the 
availability calendar to be sure the park you wish to visit is available for your date.
To locate your current theme park reservation, sign in to your 
My Disney Experience account on the 
Walt Disney World website.  Use the drop-down menu in the upper right to go to "My Plans".  Next to the Disney Park Pass you wish to cancel, select "View Details", and then you should see the option to cancel.  Once canceled, you will then be able to make a new Disney Park Pass reservation for that date.
Your visit coincides with the start of the 
EPCOT International Flower and Garden Festival!  Be sure to check out the amazing topiaries, floral displays, and the 
yummy bites and sips at the outdoor kitchens.  I know I have a huge list of snacks to try on my upcoming visit!
I hope that helps!  Please let us know if you have any additional questions.  Enjoy your visit during 
The World's Most Magical Celebration!
Anne Marie