The process by which voters can change their political party affiliation, the deadline for doing so before a primary election, and whether voters affiliate with a political party when they register to vote all vary by state.
Many states provide information about their rules for party affiliation on their elections website. You can find your state’s election website by going to the State Voting Requirements page. Choose your state, and on the following page select your election location, and “State Lookup Tools” to find a link for your state's election website.
You can also contact the Voter Help Desk for assistance.