By "DNA marker number" do you mean the paternal and maternal haplogroup assignments? If that's the case, in the drop-down menus, under your main menu (your profile number drop-down) choose "DNA". From that screen, along the top, there are five clickable boxes—choose the center box labeled "DNA Tests". For the test you need to change, on the far right side is a green button labeled "EDIT OR ENTER MORE DETAILS"—click on that and make the changes you need.
If it isn't the haplogroup information, could you be more specific about what you mean.