Keep it Open
you want to increase fico score then keep the card open. You may not need a credit card now, but when you will need one (and you will) – you could get better terms if you already have good credit. You may also want in the future to get a car loan or a home loan. Having a good credit history will make life easier for you.
In fact, store credit cards are an excellent way to build good credit because they are easier to get without a credit history.
Keep the card, use it moderately and always pay the full statement to avoid interest.