How to remove Oracle DB 11 and 12 in Windows

http://stackoverflow.com/questions/8450726/how-to-uninstall-completely-remove-oracle-11g-client

http://docs.oracle.com/cd/E16655_01/install.121/e17720/remove_oracle_sw.htm#LADBI7824

• Uninstall all Oracle components using command line uninstaller located at ORACLE_HOME\deinstall\deinstall

• Run regedit.exe and delete the HKEY_LOCAL_MACHINE/SOFTWARE/ORACLE key. This contains registry entires for all Oracle products.
• Delete any references to Oracle services left behind in the following part of the registry: HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Services/Ora* It should be pretty obvious which ones relate to Oracle.
• Reboot your machine.
• Delete the "C:\Oracle" directory, or whatever directory is your ORACLE_BASE.
• Delete the "C:\Program Files\Oracle" directory.
• Empty the contents of your "C:\temp" directory.
• Empty your recycle bin.