slimmer arms... any ideas?

Kirsti • Together for 7 years, newlyweds still trying not to conceive
Howdy ladies. I'm getting married in July and am perfectly happy with my body. My dress, however, is not. It is a bit snug in the arms, and if I'm gonna get down at the after party, I'd like to be able to raise my arms more than six inches! 
I'm open to altering the dress, but I'm looking for the free option of being a healthier human, as I could probably be a bit fitter in the arm region anyway, and this is a great excuse! 
I'd love to hear what you lovely bunch has to suggest for me!