2. Make a square selection (use the selection tool with Fixed Aspect ratio of 1.)
3. Make a selection.
4. Apply the filter 'Polar coordinates' Filter - Distort - Polar Coordinates
5. In this step use the 'Polar to rectangle' option
6. Rotate your selection 180 degrees Edit - Transform - Rotate 180 degrees.
7. Now apply the same filter as in step 4 but this time select the 'Rectangular to Polar'
8. Now simply crop and save your image.