My baby spits up after every bottle should I change her milk?

Not necesarily. Look into how much you r feeding him first. Try to make feeds of lesser amount and more frequent. Also use "reflux precautions" in which u keep babies head elevated above stomach for half an hour after each feeding, and lay him with head of crib elevated. If this doesn't work talk with your doctor to see if thickening or changing formula is the next best thing.
Depends. Spitting up is not uncommon and does not always mean that there is a problem. If your child is in pain, is not gaining weight, or the spitting up seems to be more forceful and more frequent then they need to be seen by their pediatrician. It can be very frustrating to have a spitty baby, but if they are happy and growing, the spitting will resolve with time.