Oracle Database 11g
Go to services.msc and set the below services to manual and then from CMD/ PowerShell run the following commands
https://localhost:1158/em (Enterprise Manager)
D:\Oracle\David\product\11.2.0\dbhome_1
(Oracle Home)
D:\Oracle\David\product\11.2.0\dbhome_1/deinstall/deinstall
(Uninstall Oracle)