Thinking about grad school but not sure how to start.

I've worked in University admissions for nearly 30 years, and have dealt with this question many times.

You cannot change your old GPA from your old school. Some graduate programs will average GPAs from multiple schools; others will just report that you have multiple GPAs (several data points). If one was to consider only your prior academic GPA, you look to be a risky candidate for graduate programs. You will need to demonstrate to an admissions committee that the student you were in your BSN program (years ago) is not the same student you would be tomorrow. You need to provide evidence that is more recent, and relevant to graduate study in nursing (especially since you are considering a doctoral program).

One of these points of evidence is doing well in the GRE. The GRE is designed to be an instrument to assess success in the first year of graduate study. You will need a competitive GRE score to demonstrate that you have the aptitude to succeed in grad school now (with a 2014 data point).

A second data point (and perhaps even more important) is to take a few graduate nursing classes now. Nearly every program in the country requires Nursing Research and all DNP programs have a graduate pathophysiology class in the curriculum. Excelling in graduate nursing class now (2014 or 2015) can provide clear evidence that you can do well in a graduate program now. Moreover, the faculty member of the graduate class you take now can be the academic letter of recommendation for future applications.

These three elements (new GRE, grades from graduate nursing classes, and a recent academic letter of recommendation) are additional, new data points that an admissions committee can use to consider your future application.