Nope, it's not all right to just change their names.
If anyone can recognize themselves and they perceive what is written as being a negative portrayal, you are in danger of a libel action.
A libel action is one of those strange quirks of the legal system where the accuser doesn't have to prove the case, the defendant has to prove innocence, usually the only defences is the ability to prove, absolutely, that what you have written is, absolutely, true. It is best, always, to base your characters on several people.
That is very rough and ready, you would get best advice from a solicitor, libel law is a minefield. I'm referring to works of fiction, articles and news stories are different but still need to be reported warily and truthfully to avoid court cases.