All of your post-secondary school grades are calculated into a cumulative undergraduate GPA and a cumulative undergraduate science GPA, which includes only science courses and math courses (unless it's for Doctor of Osteopathy programs, which do not include math). This is so that they may easily see your aptitude for science. However, for most applicants, the cumulative GPA tends to be a bit higher. This cumulative undergraduate GPA is one of the main standards for judging applicants for admission. So, no, you cannot "erase" or move on from any old grades. Any post-baccalaureate classes taken after your degree will be calculated into the cumGPA as long as they are undergraduate level courses. There is also a graduate GPA calculated which will only include graduate level courses.
For admission into an MD or DO program you will need to have an undergraduate GPA close to 3.5 or higher. Then, you will need to take the MCAT. A competitive score varies by program. DO schools tend to accept those with scores from 26-28 and MD schools like 30+, in general.
With your previous degree, you probably have ~130 credit hours of a 2.5 GPA. You will need to figure out how many post-bacc classes you can take to raise this significantly. You should really get it to at least a 3.0. However, your journey does not stop there because you will not to further prove that you can succeed as a student. This means applying and being accepted to a Special Masters Program where you compete with current med students as an "audition" for the affiliated med school or other schools to which you apply.
Alternatives to the SMP include a very high MCAT score. This would be 35+. Or, a very high MCAT score and a very high science GPA.
Since your degree is in business, you will need to take the med school pre-requisites, which you may know are 1 year each of biology, chemistry, physics, and organic chemistry.
ADDITIONALLY, medical schools like candidates who have explored medicine as a career in-depth, so you will need to complete significant healthcare volunteer experiences with patient contact. Medicine is also a dynamic field, and many strong applicants have research experience. Combine these activities with some interesting hobbies, life experiences, and non-clinical volunteering, and you may become a well-rounded applicant.
As you can see, it is a very long road. You must first understand the process and decide whether or not the committment is worth it to you. Have you shadowed any physicians? One more thing: you will need to write a detailed personal statement for your application answering the question "why medicine?" This is of particular importance for non-traditional students such as yourself, who have left one career for another.
Anyway, I hope this helps. I apologize if it is redundant to anything you already knew. Good luck and let us know if you have anymore questions.
