You did not say what state you are from which is a key fact. States get to set their own primary date (within the window authorized by the two national parties); so different states vote on different days.
Additionally, at the present time, we are still over seven months away from the first official vote in any state.
Between now and when your state might vote, two things will happen to narrow the field. First, some candidates will simply find that they are unable to raise the money needed to compete in fifty state contests and are not gaining traction in any state (other than possibly their home state). These candidates will drop out between now and December. Second, if you are in a later state, candidates who do poorly in the early states will drop out when it becomes clear that they are trailing. (Voters in the second round of states tend to drift away from candidates who did poorly in the early states, and money tends to dry up as donors move to the candidates who seem to have a chance.)
If any candidate that you support is still on the ballot by the time that your state votes, you are free to vote for that candidate. And, if you think that one of the frontrunners is a weak general election candidate, you are certainly free to vote for one of the other contenders. .