How do I? That's a crappy thread title. In the future why don't you think of better ones that actually describe your question and thread your starting. Thanks.
And as for your question, just set a new password if you want one. Unless you can decrypt the hash in the /etc/shadow file, you won't know the password. And it's probably logged you in as root.
cat /etc/passwd for a list of system users, root and any others that might be around. Check /etc/shadow to see if they have a password.
PS. I'm changing your title for you since you can't, take my advice in the future, make better titles or get slapped around by members and moderators on this forum.