If your stepmother has a life estate she could convey her life estate to you by deed. If the deed says something to the effect of You as owner, subject to a life estate in Stepmother...or Stepmother as to a life estate, and You as remainderman, then once Stepmother conveys her life estate interest to You, then by doctrine of merger You own in fee simple. You should have a real estate attorney verify the manner in which title is held, and prepare the deed accordingly.
Ms. Hatley gives very sound advice -- have a local lawyer competent in real estate law review the current deed and prepare the appropriate documents. Getting them wrong will cause you a world of problems, and getting it done by a lawyer will cost you less than treating a cold.
As Ms. Hartley said, your stepmother can deed her interest in the property to you. If your stepmother is living in the property now and you do not move into the property, you will lose the homestead exemption for tax purposes. Your stepmother's deed to you will be subject to the rights of any tenants that are currently occupying the property. This is something you should discuss with an experienced real estate lawyer in your area. Your lawyer can advise you on the best way to proceed and any potential pitfalls.
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.
For the protection of both of you, she should be independently represented by counsel in the course of her giving up her life estate, it should be established that she is of sound mind and that she is voluntarily giving up a valuable asset. Also, if she is living in the premises, she should understand that once she gives up her life estate she could then be removed from the premises forthwith.