What is the meaning of "change a raven for a dove" (line 114)?
The lines you cite are in Act II, Scene 2.
First question: what Lysander is saying is that loving Hermia (who he used to love) instead of loving Helena would be like loving a crow instead of a dove (this is saying a crow is ugly compared to a dove). What he's literally saying is "who wouldn't trade a raven for a dove?"
Second: it's ironic because his reason has nothing to do with why he now "loves" Helena. He loves Helena because Puck has put the potion on his eyes and she was the first thing Lysander saw when he woke up.
As to symbolism in writing, a raven represens a sinister creature, or a bad omen. It is midnight blue-black and it's hair is portrayed as think and prickly and its expression is mean or non-existent, as if it could care less about anything excpet the mission it is on at the moment. The dove, on the other hand, represents peace, an extension of understanding and care and concern for others -- totally opposite character of the dove. The irony of Lysander's love for Helena is that he is under a spell when it happens to him, something which takes him away from his "true" love and gives him over to a love that would not have happened in a natural state. The "strange dream" is Lysander's intoxicating love for Helena, when his true love was for Hermia. Or maybe it is Demetrius who is the "raven" -- either way it goes, someone is being forced to be with someone else that they do not love, so the contradiction in all cases is apparent. It is as if the "raven" (Helena) has been swapped out for the "dove" (Hermia), and if something is not done to intervene with this "bad dream," (what we might call a nightmare) he may be resigned to a doomed fate of being in love with someone not of his own choosing.
Well the first question, the change a raven for a dove, can relate to a person's hair color or skin complexion