Is it possible to replace just the screen?

This is possible but only if the touch screen still works,. If it doesn't you will need the digitizer as well. While it is possible though, it can be very challenging especially with large screens. The glass is usually glued to the LCD, which needs to be heated and then pryed apart without breaking the LCD. Afterwards you must glue the new glass on with LOCA glue, which can produce some less than satisfactory results if not done carefully. The LOCA glue needs to be hardened with a UV light as well, but these can be easily purchased.

Hope this helps.