Often, it's just a matter of changing the battery, and usually our keyfobs take a simple and inexpensive button battery. If you don't know how to open your keyfob, look in your owner's manual. If you don't have an owner's manual, then try this link: https://www.youtube.com/watch?v=DhPsIhxcf64.
Finally, if neither of those work, your local Chrysler dealership can change it for you for a nominal fee that usually less than $15.