Yes! On Monday of each week, you'll receive an email with following week's meal recommendations. In the email, there will be a link to the page where you can swap your meals. You have until Wednesday at 11:59pm PST to make changes. Otherwise, the recommended meals will be shipped.
You can also login and go to your Meal Plan Preferences page. On the right side of the page, you'll see a calendar. Hover your mouse over the week where you'd like to swap meals. Click on "Change Meals".
Note that meals can only be swapped after you have received the "meals for next week" email.