at the top of rsbandb forums click on profile, look at the top of your profile, it will say enter current password and so on. So enter current password, then enter a new one below that, then re-enter the new one to confirm it, scroll down and click on submit..
rs pass: on
http://www.runescape.com scroll down till you find the section with forums, account management and so on, click on account management, and log in. it will bring you to a page where you can change settings on your account, in the top right you will find info about changing your password. click on change password, enter current, enter new, re-enter and confirm new.. allow it to process.