Accepted but thinking of reapplying

<p>I was accepted to UW in march 2011 but I decided to go out of state. I have been thinking of coming back and I would be able to get in state tuition (since out of state tuition at other school is 30,000 and killing me). I had a 3.65 gpa when i was accepted and i currently have a 2.5 at my current university. since i was accepted would i be able to go back with out reapplying (as in does uw have a period where you have 12 months or so to take your acceptance with an updated transcript) or would i have to reapply again. Also, if i would have to reapply would my odds of getting back in be good and would the university hold it against me that i turned it down?
Also, the reason why the current gpa is so low as i was majoring in engineering at my current school but it was too hard so i switched to philosophy and am perusing law. my first semester grades were horrible but my second were brilliant A’S AND B+. Also, when I got into UW i got into the engineering program so would my current switch of majors look good or bad?
Also, should I possibly wait another semester or year to apply again?</p>