Creating a poll and being able to change vote

Hello, So I am creating a polling like app, and I’ve gotten it pretty far where with only one vote per user, but I need help in letting the user change their vote. Right now, I have one solution, but I am not sure if it is practical. I have one table, and it has a question ID, a user, and the answer field. because it is multiple choice, I just use a count to get the total of each selection. I do not now how that will work if there were large sets of data. The other way is similar to how the tutorial works, where I have one table that has one column for the question, an 4 columns from the results and adds a +1 every time a corresponding button is hit. I also have another table that stores the user and the actual result of the vote and the question id. With this one I assume that I should be able to find out what they voted for, subtract one from that column but I am not sure how to go about that.