To become a sales manager you will need proven experience in sales, with a good record of achieving targets.
Some companies may prefer you to have a business-related BTEC HND or degree, but your experience and track record are usually considered more important than your formal qualifications.
It may also be an advantage to have work-based qualifications in sales, such as NVQs in Sales, or qualifications from professional bodies such as: Chartered Institute of Marketing; Institute of Sales and Marketing Management (ISMM); or Managing and Marketing Sales Association (MAMSA).