Your rights are governed by the terms of your lease. If each of you had separate leases with the landlord, it will be more difficult for you to prevent the change in roommates. However, if all three of your are named in one lease, it may be that any assignment or sublease would require all the of the original tenants to sign. If you are unsure of your rights and responsibilities under the lease, you should consult an experienced real estate lawyer in your area.
Disclaimer: This answer is provided for informational purposes only, does not constitute legal advice, and does not create an attorney-client relationship. Actual legal advice can only be provided after completing a comprehensive consultation in which all of the relevant facts are discussed and reviewed.
A lot depends on what your lease states. It is standard for there to be language allowing a sublease so long as it is approved by the landlord. However, your situation may require the other roommates to agree as mentioned in the other answer to this post. I'm in Tallahassee and will be happy to discuss further with you by phone on Monday (4/30). I do represent a few landlords in Tallahassee, so before we get too far into this, I'll need to know who your landlord is. Don't post it on Avvo. You can simply tell me by phone (668-7849).