I would also recommend that when you send in the form you might also include a brief letter (no more than a page) delineating that UD is your first choice and also including some additional comments about your reasons why and, as appropriate, what you feel you could contribute (I don't mean monetarily) to the unversity community. Some people did this last year and did feel it helped them get in (obviously no guarantees).
I would caution you about pursuing the change in major recommendation. While it might work (actually it did work for a friend of my D who was waitlisted and had planned to change her major anyway, and they accepted her the next day after she contacted them) it may be extremely difficult to transfer into accounting from undecided (this is a very popular major at UD). So if you are considering doing this just be aware of the risks.
If I remember correctly they began to accept students off the wait list last year in late March/early April.