a) did you at any time sign anything that stated that you were working with the first agent and that they were representing you?? You may have done it as part of the contract package without realizing that you were doing it. If so, the first agent, who introduced you to the property and who wrote the first contract can insist on being paid a commission for procuring cause even if at this point in time you switch agents and go with a different agent because you don't feel that the first agent is protecting your interests. Keeping this in mind, many second agents, knowing that you have been working with another agent (and have already gone to the point of writing a contract with that other agent on the property) will be very concerned about their own legal standing in the overall situation and whether or not they will be paid or if they will end up doing all the work, then the first agent will complain to the Board of Realtors and the MREC and they will rule that the first agent as procurring cause will get the full commission (it has happened). As a result, the second agent may offer the first agent a referral fee (ie a payoff) in order to essentially get them to release you to the second agent with "no strings attached".
I would suggest that, especially since you are staying with the same brokerage, you ask to sit down with the broker and discuss with the broker why you are switching agents and that you want to be released from any contract you have with the first agent. Put it in writing stating that you want to be released from working with the first agent and state why and present it to the broker. You need to do that BEFORE you sign anything stating that you will be working with the second agent.
If you are going on to another home, it's a lot cleaner, since then there is no procurring cause if the first agent hasn't sent your information on or shown you the new home as there is with a home that you have already been shown. With a home that you have already written a contract on it's really messy, legally for a second agent to get involved.