I would break them out of the holders and frame them.
But to better answer your question, you'll want to store them in a cool dry place that is away from any significant light source (especially direct sunlight). I know that's a vague answer, but the specific way you store them is up to you.
Are you looking to store them away for safe-keeping, or have them on display in plain view? The answer to that will dictate the storage method that best suits you. There are good options either way...