Waiting it out or contacting, for job interview?

I received an email from XYZ company about being considered for a second round interview. My problem is that, in the email, it states that they'll contact me within 2 weeks and its already past 4. Should I contact them back or just wait it out? I don't want to wait much longer nor do I want to bother them in the middle of the decision. What should I do? Thanks again for the help!