Although I usually prefer to answer questions right on this page, pruning and training boysenberries (which are treated the same as blackberries) is complex enough that it makes more sense to offer you a few links to look at. I've attached links to instructions from Cooperative Extension Services from different states. It's possible that the state you live in has instructions better suited to your region. To find them, I suggest doing a web search on "boysenberries pruning +university". Omit the quotes but do include the + sign. The Cooperative Extension Service is the educational outreach branch of the state's main agricultural university, and their publications are research-based.