I want to know which specialization you chosen for work and which area you like to choose. If you go with HR - you can go with Diploma for 1 year.(eHRM, SHRM, Labor Laws etc) or go with Software ERP's like SAP, Peoplesoft, Oracle HRM etc.
Marketing - Experience plays the vital role and also you can take International Business, Export and Import in Diploma.
As Mr.Mudassar Shaikh told you have to get experience and go with knowledge.
All the Very best...!
I agree with the comment that job and career development should go hand in hand. You learn maximum while doing the work In my opinion you should not quit and continue to work. Please make a list of the things you would like to learn, areas of HR where you would like to gain practical experience/ exposure and the competencies you would like to acquire. Then keep on doing short courses one after the other. There are lot of consultancy companies offering short courses. Alternatively, you may take the services of a career coach.
We offer short practical courses in HR, short courses to develop work related specific competencies, and career coaching services. While you continue to work you can take short courses on practical HR work and career coaching for developing career plan and relevant competencies from us.
Manager - Operations