It depends on what you have done with OWL:
If you just configured it by using the GUI and didn't use file operations, i.e. moved or added files, then you just need to press the RESET button (on OWL-3G at the front, on OWL-LTE at the back). Pressing this butten resets the device such that the "normal" configuration and the scripts are deleted. As result the device can be reached by port ETH0 with IP 192.168.1.1 with the default login and password.
If you moved or added files, or edited files then you need to make a firmware update. The update can be done with the same firmware release.