In terms of content, Mathematics Advanced is naturally more difficult than Mathematics Standard because the topics and the main concepts within the topics are more complex. In that sense, if you drop to Mathematics Standard, you should find it less difficult. Of course, even with the lower difficulty, you must still study regularly to achieve the best possible results.
Mathematics Advanced scales better than Mathematics Standard, which means that Mathematics Standard students typically need to achieve a higher overall HSC mark in this subject to match the same contribution to their ATAR as that of a lower overall HSC mark achieved in Mathematics Advanced. With that being said, if you intend to study regularly for this subject, as well as addressing areas of improvement as they arise, you can definitely maximise your results in this subject, resulting in a good contribution to your ATAR.
Another important factor to consider in making an informed decision is whether you intend to study a university degree that treats Mathematics Advanced as assumed knowledge or a prerequisite. If that is the case, you may need to either reconsider your decision to drop or find a way to familiarise yourself with Mathematics Advanced before you start university. If that is not the case, then you will not need to worry about this.
I hope this helps!