Get out of IT. Learn portfolio management from the experts, such as CFOs and actuarial scientists. Take a class.
Read Harry Markowitz’s Portfolio Selection: Efficient Diversification of Investments (Blackwell Pub., 2nd ed., 1991).
Start small. Just trying Level 1 (see Page 56) will yield results.
Read books or white papers about portfolio management written for IT. The term has already been widely abused, so you may be reading about something else entirely.
Trust a vendor that says it will sell you portfolio management. PM is not an off-the-shelf concept.
Try this with a highly distributed budget. Centralization is implicit, starting at the most basic level.