help to correct grammer

(Firstly, your point - to get a higher salary job for supporting you to apply an external course - is not sufficient. You should show more your strengths to cope with the job.)

I have more than 6 yrs experience working as Clerk. I want a job can offering me an advancement opportunity. I have strong communication, administrative and clerical skills, I am familiar with the operations of the company, also, I feel that I can take on more responsibilities. My broad background makes me an excellent candidate for this position. In order to enhance my business communication skills, i am going to take a Diploma in Business course in coming May. I believe that if i sucess to promote as Senior Clerk, it would provide me with the ideal opportunity to expand my career path.

你的grammar真的很爛....
如你想說已做了6年文員(及現在繼續做....) 應該這樣寫 :
I have been working as a clerk for more than 6 years.
另外, course fee 沒有 s 及不是 high-priced, 應該用expensive.
此外, 文章完全給人感覺的是, 寫文章的人, 英文程度很底, 以及用了很多中文轉譯... 以下是我的提議 :
I have been working as a clerk for more than 6 years. Owing to have a wider vision, I have applied a Diploma in Business for improving my knowledge. It does not only give advantage to me, but also help my work. However, the course is so expensive that I cannot burden under my present payroll. Therefore, I have to apply a job with a higher salary, which can support my fee.

I've been a clerk more than 6 years. Naturally I want a promotion. So I'd like to advance myself by studying a course. I also want to take the Diploma in Business course in May. Since the course fees are expensive, I want to apply for a position with higher salary that will help me to pay for them.

2008-03-07 04:35:58 補充：
You may want to replace "a course" with the actual course name.

I have been a clerk more than 6 years. Normally(can replace by actually if you wanted to mean 實際上), I wanted promotion, so I must need to improve myself by studying a course first. At the same time, I am trying to apply a higher position and salary for support course fees. Afterward, I will go to studying a diploma in business course incoming on May. This ocourse fees is so high-priced. Therefore, I need to get the salary is higher than current salary. Otherwise, I am feeling under pressure.