You should change your modeling photos,comp card and headshot every 6 months. But it also depends on if the card you have is working for you or not?
I have gone through so many compcards and headshots over the years. Really it is good to have a few different selections. ( I always suggest www.compcard.com for cheap cards).
Here are some signs that you need a new compcard and headshot:
For a headshot: Does the photo represent the jobs you want to get? Are you showing the face of someone that fits the roles, auditions and castings you are going to? If you are trying to portray the girl next door but your look is too sexy then you will not get booked.
Is the shot straight on to the camera and do your eyes speak? Eyes are a great marketing tool, and your eyes in a headshot should speak and emotion.
For a compcard: Are you showing the photos you need to get the jobs you want? Are you showing shots that are sellable? Do the shots involve energy? A Product? Do they look like ads and editorials?- even if they aren't, do they still have the vibe of an ad or editorial or ad campaign?
Are you showing a smile. The smile is the most important marketing tool a model can use. Many girls forget the smile too.
Are all the photos on your card showing a new theme,look, and style? If you hair is long, do you have a shot that shows it both up and down? Are you showing the same photo basically in all 4 pictures or are they different? Do you have energy in your shots? It is good to have at least one energy or interaction shot of you DOING something. Riding a bike, running, walking a dog, laughing, drinking coffee, even doing your hair, putting lipstick on.
Test out your compcard for a few months, mail it to agents, if you don't hear back it might not be YOU, it might be your photos.