You'll need to do a qualification that is recognised by one of the professional organisations for acupuncture, for example:
The British Acupuncture Accreditation Board is an independent accreditation body, and has approved several courses that lead to membership of the British Acupuncture Council.
Courses are offered at different levels, with some going up to degree. Each body sets its own course entry requirements.
If you're a qualified healthcare professional, like a doctor or nurse, you could train in acupuncture through the British Medical Acupuncture Society (BMAS).
Members of the BMAS are regulated healthcare professionals who practise acupuncture in their professional practice.