When you first sign up for a job seeker profile, you'll be prompted to upload a resume file to help get you started. If you didn't do this, and wish to go back and upload, you can do so with the click of a button.
After logging in, click Profile on the left menu to open your profile page.
In the top left, you'll see a blue button that says "Replace My Profile".
Clicking this will clear your resume of all contents, and let you start from scratch with a resume upload.
Again, keep in mind, this process will erase all resume information you currently have. Be careful!