Expert Advice from wedding guru, Sharon Naylor

Answer:

This is easily solved :] Just pick out a great card stock or colored paper that coordinates with your wedding invitation, and print out individual inserts that say, "Change of plans! The reception will take place at (name of site), (address), (website)", and put a reminder of your personal wedding website URL so that guests can keep up with your news.
I like to make this a brightly-colored paper insert, and print it out on the home computer using black font if the invitation print is black, or color-match your print, so that it looks nice but still gets guests' attention.
And since some guests may misplace this insert during the weeks leading to the wedding, it's a great idea to do a mass e-mail to all of your attending guests, reminding them of the new location a few days before the wedding.

Now here's a question for you...this new location is near the old one, right? Because if you've changed to a new city, or a destination locale, guests will need enough time to make their travel plans. So that will require an email to them now. This only applies if the new site is far away...