Lost password

I downloaded the Oracle Database 11.2g on Linux. I forgotten the Oracle Database password and I cannot see the tables. Whenever I run SQL statement then I gets error message table does not found. I want to use those generic tables which had supplied by the Oracle as default when I downloaded the software. Please help to use those tables for the practice.

Would you please help me in de-installation and re-inatation of Oracle 11.2g step-by step procedure on Linux plateform. It is very urgent for me. Thanks!

Its a complicated way by which you can recover your password.
See the Discussion forum for more details:
https://forums.oracle.com/forums/thread.jspa?threadID=555748

I recommend you to de-install and re-install again.
Make sure you note all the settings and password in a NotePad file for future reference.