uploaded image not displaying in ruby on rails app

Hi I am using paperclip for image uploading. the thing is, when the user login with fb, it is displaying the profile picture from fb, once he is logged in, he can change the profile picture in the app. but the changed picture is not displaying. and i have default picture stored, that is displaying for the users registered with email. How can display new uploaded photo.

My usermodel is,

   has_attached_file :avatar, :styles => { :medium => "300x300>", :thumb 

=> "100x100#" }
   validates_attachment_content_type :avatar, :content_type => /\Aimage\/.*\Z/


   def self.from_omniauth(auth)
    where(provider: auth.provider, uid: auth.uid).first_or_create do |user|
        user.fullname = auth.info.name
        user.provider = auth.provider
        user.uid = auth.uid
        user.email = auth.info.email
        user.image = auth.info.image
        user.password = Devise.friendly_token[0,20]
        user.skip_confirmation! unless user.confirmed?
      end
  end

My application helper is

module ApplicationHelper
def avatar_url(user)
    if user.image
        user.image
    else
        "/images/missing.png"
    end
end
end

My edit view

<div class="row">
            <label class="col-xs-4" for="avatar">Profile picture</label>
              <div class="col-xs-8">
                <%= f.file_field :avatar %>
              </div>
          </div>

My show view is,

<%= image_tag avatar_url(@user), class: "avatar-full" %>