After changing the code.
Step 1.Go to Admin->Repair->Quick Repair and Rebuild. Make sure you have given username and permission for the files.
Step 2. Go to Studio ->Module->Layout->edit/detail View. Now rearrange the columns based on the new 4 column layout
step 3. Save the layout. Repeat only step 1.
This will change your from 2 to 4 column.
Thanks