Our local MLS contracts give the original agent some protection if you were to sell it on your own after the expiration of the contract but if you relist with another Realtor in Champaign County you get to "start fresh".
Your only obligation is to pay the listing agent a commission if you sell it to someone on your own within the number of days specified in your contract. If you list with a new agent, then there is no obligation on your part. If you have done what your Realtor asked and you still feel that your property has not been marketed sufficiently or that he/she has not had enough communication with you, then it might be time for a change. Above all else, you need to have a good rapport with and trust your agent. We are in a unique market situation right now, so the "team" (you, your lender, your attorney, and your agent) needs to be on the same book and page more than ever before.