Normally, there should be no reason to change your password or PIN. But there are a few cases where it's a good precaution. For example:

• You notice something suspicious on your PayPal account.
• You suspect that someone you don’t trust has your password.
• You notice something suspicious in your email account or other online accounts.
• You have recently removed malware from your system.

You can change your password settings under section " Change Password" located on upper right corner of website . This section will be visible as dropdown option under your "User" Section.

Your email id used at the time of signup will be your username.