You can apply for a researcher role by clicking on "My Account" then "Apply for Role". Research roles are only granted to people who are actively participating in the RS2 project, so unless you've made some posts to the Forum, don't expect to be approved.
If you are an authenticated user, you can post and reply on the Forum, but not much else. If you are honestly interested in trying to understand and contribute to the RS2 research project, you can apply for the "Researcher" role by clicking on "My Account" and selecting the tab, "Apply for Role" and apply for the researcher role. Researchers can create blog entries, books, stories, polls and videos in addition to forum posting.