Hi Diane,
You must be getting excited for your vacation! I love kicking off fall with a trip to the Walt Disney World Resorts!
Unfortunately, you can not change out the sofa for another bed at Saratoga Springs Resort and Spa. You do not even have the option of adding a roll away bed because these are not offered at this resort.
If you want to keep this reservation, your daughter will need to have the bed and someone else will need to use the sofa bed. I will say the sofa bed in the two bedroom suite was comfortable when I stayed there in 2012. They must have changed it out because when I stayed at the studio, the bed was uncomfortable back when the resort opened. However, everyone has different needs.
Another option is to change locations.
Old Key West offers two queen size beds in its deluxe studios. The rooms are also bigger at this resort.
Some other great resorts with two beds are
Yacht Club and
Beach Club,
Port Orleans Riverside and
Port Orleans French Quarter.
Wishing you a magical vacation!
Beth