When we upgraded our website we also had to install a new backend system and database. If you had registered successfully before just go to the USER REGISTRATION module in the right column and access the 'Lost password?' feature. The process is self-explanatory.
When you register and choose your user name and password make sure that they contain only regular alphanumeric characters (a-z, A-Z, 0-9) and no spaces in between. Also, see that they contain at least 6 characters (or more).