Docker updating image along when dockerfile changes

Docker updating image along when dockerfile changes

I'm playing with docker by creating a Dockerfile with some nodejs
instructions. Right now, every time I make changes to the dockerfile I
recreate the image by running sudo docker build -t nodejstest . in my
project folder however, this creates a new image each time and swallows my
ssd pretty soon.
Is there a way I can update an existing image when I change the dockerfile
or I'm forced to create a new one each time I make changes to the file?
Sorry if it's a dumb question