To transfer your Bar Council membership from Patna to Delhi, you need to apply to the Bar Council of India using the prescribed form. The Bar Council of India will then direct the removal of your name from the Patna roll and its entry into the Delhi roll. This process is governed by Section 18 of the Advocates Act, 1961, and no fee is involved. While practising advocates can practice anywhere in India, transferring your enrolment is not mandatory even if you shift your residence.