Hello @Rachel216,
To change the minimum number of nights stay during some period do the following.
Go to your calendar and click on "availability settings"
Then click on "Reservation preferences".
Look for "Add a requirement for seasons or weekends" at the bottom of the page and click on it.
Click on the "During" box and select "Specific dates" and enter the start and end dates.
Enter the minimum nights stay you want for that period and click on save.
You can then add more minimum nights stay requirements for other periods by selecting "add another requirement" in the "reservation preferences" window.
Steve.