HI, I need help regarding my username and password I sort of forgotten those. How can I change them? Is there a way, other that reinstalling?
Yes, there is. You don't specify your OS nor XE version. Anyway you can set the XE environment, for example the following refers to 10g XE on Windows (OS prompt) :
sqlplus / as sysdba
At this point, assuming your OS user is member of ORA_DBA group, you can do what you want, for example change your user's password
SQL> alter user <your user> identified by <new passord>;
Or you can create new users : for this one please check the documentation : http://docs.oracle.com/cd/B19306_01/server.102/b14200/statements_8003.htm#i2065278