use warnings;
use strict;

while (<DATA>) {
    s/"(.+?)"/"NEW"/;
    print;
}

__DATA__
This is line 1 "hello there"
the is line 2 "goodbye, take care"
this is line 3 "Jump, fox. Jump"
[download]

prints:

This is line 1 "NEW"
the is line 2 "NEW"
this is line 3 "NEW"
[download]