Sometimes you come across a volunteer, MSA president, or masjid board member who is flat out incompetent. They're well intentioned, but no matter how hard they try, they'll just never cut it. They want to help so bad, but their help means double the work for you because you have to hold their hand through the process. Addressing incompetency is a two-step process. First, is fixing your attitude. Second, is actually addressing the incompetence.
Many times, people just need a nudge. Treat them nicely and gently - the same way you would want to be treated if the roles were reversed. Don't forget your own incompetencies in different aspects of life.
Look closely at what issues this person is having. Can the problem be fixed with education or mentoring? The problem we face in Islamic organization is not only a lack of time to mentor, but an unwillingness to do so because of territorialism. That's a lethal combination. We all got started with some level of education and mentorship. Step up and provide it for someone else.
Leadership means doing whatever you can to provide what that person needs to be successful. In some cases though, a person will never 'get it' no matter how hard they try (seemingly rare). In this case, try channeling their energies into something they are better suited for.
If, however, you are dealing with a volunteer (or even employee) who is just flat out lazy and won't take any steps to improve, then you need to find a way to politely and amicably help them move on to something else.