If the seller does not lower the price to the appraiser value and you still want to buy. The lender will lender based on the appraised value and you would likely have to put more down if you still wanted the house.

Speak with your Realtor and have him/her contact the listing agent. As long as you have not removed your contingencies in writing you should be able to renegotiate the purchase price with the seller if they are willing. The seller however does not have to agree to sell the home for the appraised value.