First off, make sure you have all your important data backed up to an external drive or SD card and then reboot you EeePC. Please note that any additional software that was installed will also be erased.
When the EeePC reboots press the F9 key over and over under you get to a black screen that has an option to “Restore to Factory Settings”. Select that option and wait about a minute or so and the EeePC will reboot itself.
When the EeePC reboots it will ask you to enter a username and password just like it did when you took it out of the box, and then boot to the original “easy” desktop.