You can't. Those restrictions probably run with the land. There's a small possibility the restrictions can be changed if you can prove to a court they don't serve their original purpose, but this depends on state law (I'm not admitted in AL), so you may want to consult an attorney, but usually such conditions in a deed are binding on successive owners (as are similar conditions requiring a certain square footage of home or dollar value; only restrictions which violate civil rights of protected categories can be overturned -- those dealing with race or religion which were once quite common -- especially in the South although not infrequent everywhere before more pervasive zoning and government control of land use and development).
This answer is provided under the Avvo.com “Terms and Conditions of Use” (“ToU”), particularly ¶9 which states that any information provided is not intended as legal advice or to create an attorney-client relationship between you and me or any other attorney. Such information is intended for general informational purposes only and should be used only as a starting point for addressing your legal issues. In particular, my answers and those of others are not a substitute for an in-person or telephone consultation with an attorney licensed to practice in your jurisdiction about your specific legal issue, and you should not rely solely upon Legal Information you obtain from this website or other resources which may be linked to an answer for informational purposes. You understand that questions and answers or other postings to the Site are not confidential and are not subject to attorney-client privilege. The full Avvo ToU are set forth at http://www.avvo.com/support/terms . In addition, while similar legal principles often apply in many states, I am only licensed to practice in the State of New York and Federal Courts. Any general information I provide about non-New York laws should be checked with an attorney licensed to practice in your State. Lastly, New York State Court rules (22 NYCRR Part 1200, Rule 7.1) also require me to inform you that my answers and attorney profile posted on the Avvo.com site may be considered "attorney advertising" and that "prior results do not guarantee a similar outcome".
Presuming that the land is in the county and not within the municipal limits of a town, then the issue would be determined on who was the original grantor of the deed and when the restriction was added. You would need an attorney to review the matter as well as a title search. IF the deed issue can be resolved, the actual subdivision aspect occurs by filing with the appropriate governmental authority (Zoning Board in a town, County Zoning authority for the county, etc.) to apply for a subdivision. You have to meet their respective ordinances and requirements. I spent 7 years as a chairman of zoning, you can contact me if you can not find a local attorney to help you and I will help you to find someone.
First I would suggest checking with your local jurisdiction's (e.g. city, county, etc) and see if subdividing the land into one acre is allowed under local zoning rules. If it is not, this is likely not worth pursuing because you have two difficult battles to fight - not just one. If a one acre lot would comply with local zoning requirements, you should consult with an attorney to discuss ways that this property restriction might be removed. In some situations it might be possible, for instance in Washington state if the one acre was gifted to as part of the grandfathers will after he passed away the land would automatically be subdivided into a single acre. In addition, there are instances wherein if a permanent restriction on use of property restricts it so much that it cannot be used that a court will overturn the restriction. An attorney with more information on the case should be able to walk you through this and tell you if there are any ways to remove the restriction.