H4 to H1b in I539 queries and suggestions

I have a query. My wife is on H4 and in US and recently her H1b got approved. when I539 change of status needs to be applied or It was applied during H1b Filling? I got so many answers from different people. Want to know only by applying I539 after H1b approval will change her status from H4 to H1b.

Typically the attorney will file H1B with change of status. This is requested in the form I-129 so you need to check with her employer’s immigration lawyer.