You have a migration script
if that does not work then your best option is to recreate all content-types how they where in v3 in v4 and using the v3 api to request all data and then posting it to the v4 database
You have a migration script
if that does not work then your best option is to recreate all content-types how they where in v3 in v4 and using the v3 api to request all data and then posting it to the v4 database