You can complete a balanced selection of accredited v3 Service Capability or Service Lifecycle modules and successfully pass the module exam(s) to attain 17 or more credits
Or
You can obtain additional credits by achieving additional v2 Practitioner certifications to attain 12 or more credits (under the v2 Scheme requirements, so long as the certifications remain publicly available) in order to become eligible for the v3 Managers Bridge Certificate
You will also need to attend the v3 Managing Across the Lifecycle course through an accredited training provider and successfully pass the exam.
Depending on how many credits you hold you may have time to complete further training and examinations before the withdrawal of Practitioner in December 2010 to achieve the prerequisite 12 credits.