You can take them out of the pots, but if you cut the roots, there is a good chance your palm wont make it. They cant tolerate too much root damage and even disturbing there roots can slow there growth.
Washingtonias need lots of heat to grow fast as well as sun so maybe its not getting enough warmth. They will grow in cooler climates, just not as fast. Seedlings also grow slower than adults. It might be in too big of a pot now, but as long as the pot drains well and the plant wont rot from excess moisture, it should live to get to a size large enough to fit the pot.
Good luck!
-Alex