I think if you're interested in changing the direction of the DNC, you'll probably need to target local branches first. Ken Martin for example is the party chair of the DFL (MN org for Democrats), and got elected as DNC Vice Chair:
In 2017, Martin was elected by his peers throughout the country as the President of the Association of State Democratic Chairs (ASDC), and by that election became a Vice Chair of the Democratic National Committee (DNC). On January 21, Martin was unanimously re-elected President of the ASDC. Upon his re-election, Martin pledged to continue "our important work of strengthening Democratic infrastructure across America."
That voting process is probably what you'd want to target. He's also probably the sort of "status quo" politician that you'd want to get replaced with a progressive.