How to reduce bigger image size to small without losing quality?

I have 5236*4256 pixel image with size of 3.2 mb so i want to reduce and resize the file size without losing quality in Photoshop cs6. Basically we work for some website so we have to upload the images without losing the quality with smaller file size. we are using the save for web option but facing the quality problem some times its becoming big issue. so how to solve this quality problem.can u give me some techniques or suggestion.