Click Edit Profile, scroll to the very bottom of the page, enter your old password, and your new password twice, and click Update Password.
Don't forget to click "Update Password" to save your changes!
(Note, if you're using a mobile device, after you click the link you'll need to go to "Menu" and then select "Switch to Desktop site", as these sections can only be edited on a desktop web browser.)
If you forgot your password, visit this page: http://www.pof.com/getpassword.aspx
*Please ensure you're entering the email address registered to your account, and check your junk folder!