We don't have an expiration time for if you would like to exchange to a different color or size as long as the item is not worn or used. 
If you are still within the return window (20 days), we will send you a FREE return label, please place a new order of the one you like.  
If you are outside our return policy window, please mail it back to us with a note. We will exchange it for you, we will cover the 2nd shipping cost to you.
The return address is as below:
Sissily Designs
711 S Glebe Rd,
Arlington VA 22204
Price differences will be adjusted accordingly. 
If you already sent us an email, we will reply to you regarding your request of exchange ASAP. 
Please click HERE if you would like to send us a message.