[Ahkeith Salley]

Nope other commenters ALL wrong. what your looking for is not tilde panel expansion but actual Ram preview full screen mode. You need to reset or set your workspace to standard. Toolbar /window/ reset Standard after doing so youl notice the playback controls too the left of the interface now has the Ram Preview and frame rate options along with the Full Screen check-box.
check the box and your good to go.