heroku and amazon s3 image resizing

my app lives on heroku, and I have recently made some changes to the architecture. specifically the size of the images in users profiles has changed. like so:

//images.rb

has_attached_file :photo, :styles => {:full =>"800x800>"},
:storage => :s3, :s3_credentials => "#{RAILS_ROOT}/config/s3.yml", :path => ':id/:style'

//images_old.rb
has开发者_开发知识库_attached_file :photo, :styles => {:full =>"600x600>"},
:storage => :s3, :s3_credentials => "#{RAILS_ROOT}/config/s3.yml", :path => ':id/:style'

Is there any way I can update the size of the images that the users have already uploaded (this is a live app)?