How to change profile pic

Firstly How to post replies of replies?For example I have commented on any writer's os 'loved it' n she replied 'thanks' n I want to reply to that response of her,how cud I do that?plz ans. Secondly how can I change my profile picture through mobile.I went to my profile photo n clicked Update photo n even selected which pic I want for my profile but it didn't change.So can anyone help me.

There's a 'Quote' option. You can click on it and post your reply.