If it is the default password you've forgotten, they are listed here - http://www.raspberrypi.org/downloads/
If it is a password that you set for yourself then things are a little more difficult. It will be necessary to know which Operating System you have installed, and whether it was installed 'directly' (from a .img) file, or by using the NOOBS Installer.
How To Ask Questions The Smart Way: http://www.catb.org/~esr/faqs/smart-questions.html
How to Report Bugs Effectively: http://www.chiark.greenend.org.uk/~sgtatham/bugs.html