That is not true at all. The charges didn't change, and they weren't "BS". Donald Trump tried to leverage Congressionally authorized military aid to an ally, against their president's willingness to perform a campaign favor for him. Trump's goal wasn't to root out corruption in the Ukraine. Trump's goal was strictly self-serving. Trump was using the power of his office to coerce a personal favor that would have been of no benefit to the country at large... but rather, of benefit to himself. That is called public corruption (please see below), and it can not be allowed to stand as precedent for the acceptable professional conduct of future Presidents of the United States.
Public Corruption: is a breach of the public's trust by government officials who use their public office to obtain personal gain. It is a violation of federal law for any federal, state, or local government official to ask for or receive anything of value in exchange for, or because of, any official act.
In this instance, President Donald Trump attempted to use the office of the Presidency, to obtain a campaign favor (the announcement of an investigation into his most likely opponent in the 2020 election) from the President of the Ukraine. President Trump requested this favor in exchange for the military aid which had already been pledged. The official act was the removal of the freeze on the military aid, which Trump himself had placed, just prior to the infamous July 25th phone with President Zelensky. There is nothing "BS" about what happened, and it was proven.