It is always best to hire someone skilled to do so, unfortunately in most cases these companies dedicated to cancel timeshares usually cheat for the second time to their customers since they are vulnerable and desperate. If you are thinking of hiring them you just have to make sure you do not have to make any payment upfront.
I found this article that speak precisely about this, you should read it, that might help you to resolve many doubts:

http://www.timesharescam.com/blog/121-how-to-get-rid-of-a-timeshare/