First, head to RuneScape.com. The homepage should appear. Then, up at the top right hand corner of the screen (Seen below,) click login, and fill your account Username and Password in.
Once you've logged in, you will be taken back to the homepage. From there, up at the top right corner of the screen, click account, and then account settings.
You will be asked to login again for safety, so fill in your username and password. A screen will appear, click recovery questions, and a menu will pulldown. From there, you can adjust your recoveries.