If you didn't apply for investor status when you initially signed up as a Slated member, you can still fill out an Investor Application.
Links to the Investor Application appear in two places.
You can go to Settings, which is available via the member thumbnail in the top right corner. In Settings, Apply for Investor Status is a link within the left rail:
Also, from any other member's film page, Apply for Investor Status is a button that appears on the right rail: