If you have completed MBA in Marketing then after working as a salesperson for 1-2 years, you could have moved to the Marketing Department. Spending a time of four years is a little longer. Most of the marketing managers start their career in sales but move to their core area as soon as possible. You can try for marketing even now also but then possibly the transition could come with the reduced salary. Are you prepared for that?
Lastly, your query is not consistent with your qualification. In fact, you should be guiding others on the transition from sales to marketing.
17th January 2019 From India, Bangalore