Can i seek another appraiser? I did not like his judgement or attitude, is it possible?
Yes, you should talk to your lender about it. Remember, you're the one paying for it. In my experience and observations, I disputed the appraisal by showing my lender a Comparable Market Analysis (CMA) report (your agent should be able to pull this info), showing proof of the numbers and variables that...

Can i fire my realtor and get a new one?
I understand your frustration. The reason you're not receiving the attentive service from the agent is because, as you mentioned, you're not ready to buy and have not signed an agency agreement with her. So she's under the impression that you're not a serious buyer. Being in you're situation, it's not...