You do not need to remember the financial ratios as questions that require their use will provide the ratio(s) that you need to use in answering them. This means that, in terms of financial ratios, your focus should be on optimising your ability to interpret and manipulate them, which you can do by completing a number of practice questions that require their use. On the other hand, elements that you do need to remember include the accounting equation and COGS. Understanding and applying those should be fairly straightforward.
The ease with which you are able to remember the meaning of a particular concept can depend on your understanding of that concept. If you understand a concept well, you are more likely to be able to remember its definition and apply your knowledge of it to a question that targets it. Conversely, insufficient or complete lack of understanding of a concept can increase the difficulty of remembering its significance for you. Because of this, it is important, in the event that you are unsure of any concept(s), that you seek clarification as soon as possible. One way of ensuring that you understood a particular concept is to first study the concept, then express it in your own words. You can subsequently compare your definition or practice response to a textbook definition and sample answer respectively, allowing you to determine whether you are improving.
You should not overlook the syllabus document, as it provides a clear list of all the concepts covered under the Finance topic. You should use it alongside your textbook(s) and/or notes as you begin to study each concept, and doing so diligently and attentively, so that you become more likely to understand concepts, enabling you to remember them more comfortably. Keep in mind that this is not a simple process and can apply to other subjects, although you are definitely still able to overcome this challenge with substantial preparation.
I hope this helps!