Level four is through the door closest to the first door. You have to get 3 stars. For level six, you have to get into the room up the stairs to the left. Then you have to fight bowser, win, and he will give you a key. Go through one of the doors without stars on them near the stairs. Then go down and unlock the door. Then work your way through it until you find a door with a star on it. Go through there and you will be at level 6.
Gifts:
From SN