If you have been subpoenaed, you still must appear even if you plan to "take the 5th."
"Taking the 5th" means choosing to exercise your Fifth Amendment right against self-incrimination. That means if your statements would tend to incriminate yourself, you can invoke this right. However, if you simply "have nothing to do with it," this is not grounds to invoke the 5th amendment. Even if you are scared to testify because of what someone else might do, or you just don't care, or you don't think you know anything, etc. those are not situations where you can "take the 5th."
Are you likely to incriminate yourself if you testify honestly such that you may be at risk of being criminally charged? If so, you can plead the 5th Amendment. However, you STILL must appear if you have been subpoenaed, and you must take the stand and actually plead the 5th Amendment in response to questions that may incriminate you criminally....
this is among the most loaded and dangerous questons that you could ask, both for an attorney and for yourself. This questoin should not be asked on this site. If you are even wondering whether you need to take the 5th, you should be privately consulting with an attorney.