Well, you have the option of blocking them if itΓÇÖs just a rubbish comment with nothing but childish insults, but for the more severe ones, if you have them, is to report them.
However, if the ΓÇ£bad commentsΓÇ¥ are nothing more than positive and/or constructive criticism, which youΓÇÖll have to identify and make a judgment for yourself, then see what theyΓÇÖre trying to suggest, and just make those changes. Be careful though, some may seem like horrible comments, but generally constructive criticism is easy to pick out.
Again, anything serious like racism or threats of violence and so on definitely need to be reported.
ItΓÇÖs up to you to reply to some or all, thatΓÇÖs your call, but I wouldnΓÇÖt even waste time doing that unless you feel you absolutely need to. My suggestion would be to just block or report.