my wedding is in may and my dream gown is strapless but i arms are big.how do i lose the fat?would diet and excercise do it in time ?

Yes, diet and exercise (cardio) plus weight training are the keys to losing fat and developing toned muscles.
You have seven months to accomplish your goals and that's plenty of time (depending, of course, on how much weight you need to lose). Realistically, you could lose as much as 40 or more pounds in that amount of time if you were to lose 1-2 pounds per week.
Start a healthy, low calorie (not less than 1200, though) diet and do cardio, 20-60 minutes (depending how intense, the more intense--HIIT, the shorter the duration), 5 days a week. Start lifting weights 30-45 minutes, 3 times per week. You will definitely see a new, svelte you emerge in time for your big day.

thank you i will do that but i dont want my arms to look so muscular i want to look like my arms are thin. that might seem stupid i do want to look healthy but not like a man.ant advice ?