Did you forget your masterpassword?

• Master Password

If it is not the master password like described above and the ONLY password to Thunderbird, then it must be your email password. This is between you and your email provider. Go to their web mail or email help page and look for a link to reset your email password.

I need to change my password or Thunderbird needs to email the current one to me

No one at Thunderbird knows what your password is or will be emailing you a new one. Work with your email provider to get your password reset.