I need advice on a story im writting

I have a problem and im stumped. I have written a story almost to the middle. I think its good but not as written. I have thought of a better way to start it and write the first half. It wont change my plans for the second half. But, its a totally different start up to the half point. What do I do? Just write it from then and later change the start, or rewrite the whole damn thing

Have any of you writers here even encountered a problem like this and what did you do