Loosing weight quick.

I've booked my daughters christening for the 15th August. It's going to be the middle of summer so will be wearing a dress etc. I'm a size 16-18. I would preferable like to drop at least 1 dress size to be about a 14-16. Is that realistic in 2 months? I really want to wear a dress and feel comfortable as well as run around for the day with everyone without looking like a sweaty mess... I don't mean desperate diet fads just basic working out, walks, extra water and health eating