i should study oversea or stay

Studying in overseas of course is better in some ways and I know sometimes, you can be very stressed. I have been studying in UK for 3 years and I am a bit regrettful for coming to UK so early. I think somehow, you should stay because the HK educatoinal system has changed, it is 334 now, so at least you can stay in HK till you are F.6 and at that time you can choose to stay or go to some where else. Also, if you are leaving after F.6, you will know quite a lot of stuff that has already taught in hk, so you won't have a lot of problems later on in college or in uni.

Also, you are in F.4 now, don't you think it is too late for you to go to AU now? But if you are sure that a school has already accepted you and you can go after Christmas, it will be totally different. Also, going to overseas is not the only way to solve your problem, e.g., you can go to an international school or have some extra tutorial classes. If you are going to study in AU/NZ, and you still don't work hard, you will be even sadder because you are away from your family, you have wasted their money and you have wasted your time.

THINK VERY CAREFULLLY BEFORE YOU MAKE A DECISION !!!

if your family have enough money to send you to overseas. of course go overseas will be better. at least overseas have more choice of subjects. becuase you want to study some art subjects like photography,textile, overseas has much more choice than hk. hk is only good for business or financial subjects.
actually, you may expect several ten thousands a year on school fee, not incl daily expenses. so you better ask if your family can afford it or not. AU/NZ is ok. You should go to some overseas expo to get more information. Normally hold in Summer time.
hope can help you!