Download firmware 1.1 from the Olympus Imaging Japan website:
http://dl01.olympus-imaging.com/OLYMPUS_MASTER/FIRMWARES/0001/1440/OLY_E_144_1100_0000_0000.BIN

Create a folder called "DCOLYMP" on your SD card.

Rename the downloaded file to E1449999.BIN and put it inside this folder.

The whole process will take a about 1-2 minutes.
Make sure your camera is turned off at first. Now insert the SD Card with the firmware file.

Start the camera while holding the "OK" button.
The screen will be black and the orange front LED will turn on.
DO NOT TURN THE CAMERA OFF WHILE THE LED IS ON.

Wait until it blinks rapidly.
This means the process is finished. You can now restart the camera like you would do normally.

Attention afterwards:
You may want to remove the "DCOLYMP" folder from your SD card, so you don't flash a new firmware by accident.