Farishta is a Farsi and Kurdish name for girls that means kind, beautiful and good-mannered. It is a variant of the Farsi word Fereshteh, whose original meaning is angel.
The practice of naming girls as angels, and thinking of angels as female, comes from pre-Islamic pagan traditions, and for this reason it is best not to use Farishta as a name. It is not forbidden to use it, but many scholars dislike it because it has non-Islamic connotations. The Quran says:
Those who do not believe in the Hereafter give angels the names of females (Quran 53:27)
The verse above is speaking about the opposite practice, of calling an angel by a female name (angels are not male or female). Calling a female an angel is very slightly related to this, and for this reason it is best not to use it.
However, if someone's name is currently Farishta, then there is no need to change it, since it is not a forbidden name, it is just not recommended Islamically.