I'm not sure where you want to change the word 'very' -  is it in the sentence ... "they are very selfish"?  

In any case, I think you are right -  the words 'acutely, supremely, truly' would not be good there. Sometimes - in fact very often -  the easy word is the right one.

Remember it's NOT really a vocabulary test, even though vocab is part of the marking criteria. It's not until Band 7 that writers are expected to use less common vocabulary items correctly.  Vocabulary is more important in the Reading test in IELTS than in the writing. (Have a look at the official writing descriptors here.)

Some students try to fit as many complicated words as they can into the writing, but that's not what is required or expected, and it won't help them to get a good mark. Sure, show what you know, but it's more important to be error-free, natural and flowing and to have fully-developed ideas than to have a dictionary in every paragraph.

I think you should do a good bit better than 5.5 next time, as long as you keep sentences short and use simple vocabulary. Remember writing is not the same as speaking: eliminate unnecessary words in your essay.

Enda

I have some questions :

I went to "Grammarly" website, It suggested me to replace "very" to "supremely, truly, acutely"

but I think it's weird using that. Does it can replace "very"?

and it's my first time here. I curious that what grade I can get in this essay? (In IELTS)

I had taken IELTS before, but only got 5.5 in my writing. 

I need to get 6.5 next time, could you give me some advisement?  

Thank you very much!

Your essay has 290 words, with an average sentence length of 18 words. It's better to keep the average sentence length short. Aim for shorter sentences, and have a mix of some very short sentences with some longer ones. Don't have any longer than 20 words.

Shorten sentences

The development counties have the ability to help those poor countries; but sometimes they don’t want to give a hand to destitute nation because they are very selfish that they only think about themselves.(35 words)

Thus, as far as I’m concern, if we want our economic better, we shouldn’t just concentrate on our situation but the whole world’s economic situation. (25 words)

You can remove some words which repeat what you have said or which don't add anything.

There is/There are
These words can often be removed. They don't add much.

• There are many rich people living a luxury life while other poor people who are starving but can’t find anything to eat. (22 words) 
• Rich people live in luxury while many poor people starve.

• Sometimes they don’t want to give a hand to destitute nation because they are very selfish that they only think about themselves
• Sometimes they don’t want to give a hand to poor countries because they are very selfish.

Word Choice/Word Form

• If we want our economic better ==> If we want a better economy
• Secondly, the destitute area has many kinds of disease ==> destitute is too strong - poor, impoverished, developing, underdeveloped.
• as far as I’m concern ==> as far as I'm concerned
• If you are able to help people then you should do it, so as the development countries ==>
• If you are able to help people then you should do it, and so should the industrialized(developed/rich/affluent) countries.
• If you are able to help people then you should do it, and it is the same for developed countries.

Some good sentences!
You have some good sentences and ideas. I like "First of all, I believe that the more power you have, the more responsibility you have" and "we shouldn’t just concentrate on our situation but the whole world’s economic situation." Overall, a good essay. Just keep sentences short and simple and watch word form (should it be noun? adjective? verb?).

Hope you help some other people here on the forum!

Nowadays, We live in a society, which has big wealth gap between rich and poor. There are many rich people living a luxury life while other poor people who are starving but can’t find anything to eat. In my opinion, I support that the development countries should help the poor countries. 

First of all, I believe that – the more power you have, the more responsibility you have. If you are able to help people then you should do it, so as the development countries. The development counties have the ability to help those poor countries; but sometimes they don’t want to give a hand to destitute nation because they are very selfish that they only think about themselves. They just care about earning money and make their economic better. Thus, as far as I’m concern, if we want our economic better, we shouldn’t just concentrate on our situation but the whole world’s economic situation.

On the other hands, to help the destitute nation doesn’t mean give money to them. As an old proverb goes, “Teaching a man how to fish is better than giving him a fish.” We should help those poor countries with education, medical and agriculture.  First, Agriculture is the basic living tool; people can learn how to cultivate the food so that they won’t starve. Secondly, the destitute area has many kinds of disease, so we need to support them with medical help, which can reduce the mortality. The last is education; education is a way that helps people develop the morality and other skill such as: architecture.

All in all, no matter which country you live, all of us are part of the earth. We should help each other and make the world better.