If possible, change your clothes. But if its very hard for you, then wash the blood stains with water. But if that's still not possible, then you can pray with whatever clothe you are wearing.
but how much blood is allowed on clothe without you having to change them - for eg if you have a spot which bursts open and blood pops out - then would you have to change
what about the water that comes out of spots - is that impure too??