Can I file a provisional patent on a patented product that I have changed so it works better but still keeps the same components of orginal idea?
Most patents are for improvements to something that already exists. The new version of your product needs to be truly new and not obvious in light of everything that has ever been done anywhere. You might ask yourself if the new version still falls under the existing patent. I am presuming you are not the patent owner. Getting a patent yourself does not get you out from under the problem of infringing the existing patent.
You might be able to sell a patent on the new version to the people with the existing product or you would need a license from them if the new product infringes the old patent and you want to make it.