Or you can buy a replacement fan or fan set, for fairly cheap, and not need to break anything at all. It might help SOME, but there is no way you are going to break every other fan blade off in such a way that you actually remove the exact amount of material from each one, so there is still going to be some amount of imbalance no matter what you do. Replacing it is the only correct way to fix your problem.
What you need to do is remove one of the fans and post either a picture of the label on the back of the fan motor or the model of the fan itself, and we can easily find you a replacement fan or pair of fans if it's a model that comes with two or more fans with joint wiring.
I think the last set I found, about two days ago for...