In the expression "vi è stata", "è stata" is "passato prossimo" tense of verb "essere" (i.e., "to be"). One has to use the feminine participle "stata" because the subject of the sentence is "una modifica", which is feminine.
"Vi" is a more formal version of "ci" in the function of adverb and corresponds to English "there". That is, "vi è stata" is the same as "ci" + "è stata" expressed in a more formal way (but "ci" before a form of verb "essere" which begins with "e" is elided with an apostrophe, i.e., one says "c'è").
For instance, if you ask someone
Quando vai al mare?
the answer could be
Ci vado domani,
which means "I'll go there tomorrow" (this example is from the book Grammatica e pratica della lingua italiana per studenti stranieri by Federica Colombo; notice that "vado" is "indicativo presente" tense used to express a future action).
See these two answers for more detailed information about the different roles of the word "ci":  and .
So, the expression "non vi è stata" means "there has been not". As explained by egreg in a comment,
Non vi è stata, infatti, soltanto una modifica dei contenuti
means, "In fact, there has been not only a change in the contents".