Briefly, it depends on what sorts of philosophical issues you want to pursue. Most philosophers, including most good ones, don't have extensive scientific knowledge, and the questions they're interested in don't call for knowing lots of science. But philosophers who work on issues in physics, or biology, or psychology or other sciences need to be knowledgeable about the sciences they work on. In philosophy of physics, it's not unusual for a philosopher to have an advanced degree (Masters or even PhD) in physics. Even if s/he doesn't have a science degree, s/he will have to have acquired a lot of knowledge of the field - or relevant parts of it.
By way of general recommendation, however, the single most useful thing you can do if you're interested in philosophical issues about science is to learn as much math as you can. That can give you a serious leg up on learning the more specific scientific ideas that may be relevant to your interests. So if you have the aptitude, at the very least take some serious calculus and stats, and some linear algebra as well. And if you can do more, you're unlikely to regret it.