First : Go to menu "Module"
2nd : activate the "raw_rec.mo" this module which will make the the camera can record in raw, but I prefer the "mlv_rec" (please find the explanation on the other thread.
3rd : switch off the camera
4th : switch on the camera, and on the menu "Movie" will appear the sub menu "RAW video", press the Q to adjust as you want.
Due to the capability of 550D writing on SD card, it can not do HD.
Other possibility : make lower the "FPS" and record in HD, very useful for time lapse, or record in lower than HD and then up-res.
Good luck !