If you do have certain experience with handyman work, you can easily accomplish garage door maintenance yourself. However, you still need to be quite careful and think it through before getting to work on the door.
Before you begin the work, make sure that nobody else is using the garage door at the time. In fact, if you are worried, ensure that others know you are performing maintenance work and to clear out the area. If you have kids at home, keep them far away from the area of the garage as you do the maintenance work. You need to disconnect the opener from the electricity so no accident can happen.