If what you need is on the top shelf, use a ladder, but protect yourself!
When is it not safe to use an A-frame ladder?
A-frame ladders have limitations that relate to their function and stability. Understanding these limitations will help you evaluate in what places and situations they can be used safely.
A-frame ladders are only suitable for use on surfaces that provide a level and solid support for all four of their feet. Before positioning the ladder, make sure that the surface is firm, level, and free of debris. Before ascending the ladder, it is important to determine that its frame will not twist or rock when weight is transferred from one side of the ladder rungs to the other.
Do not try to compensate for an uneven surface by placing spacers made of things like wood or bricks under the feet of the ladder as these can easily work out from underneath the ladders feet and throw the ladder and you off balance.
Make sure that the A-frame ladder that you use has sufficient height to allow you to safely access the elevated location you are trying to reach. It is never safe to stand on or above the second from the top rung on A-frame ladder. You should see that warning clearly indicated on that rung of the ladder.
If the ladder you have is too short, get a longer one, or talk to your supervisor about a different solution. Never sit on the top step of an A-frame. Your center of gravity will be too high and the ladder will be very unstable.
A-frames ladders may be convenient for quick and temporary access to an elevated location, but they are not stable work surfaces. You should make sure that they will be stable on the surface they will be placed on, minimize your time on them, and be realistic about what you can safely accomplish while standing on one.