- Open the registry editor and navigate to the key
- Click on "Edit > New > DWORD-Value". Name the new entry as "Thumbnailsize".
- Double click on the entry, select the "Decimal" radio button and enter a number between "32" and "256". Default value is "96".
- Enter a larger value to increase the Thumbnail Size and Smaller value to decrease the Thumbnail Size. Confirm the change by clicking on "OK". Restart Windows Explorer for the changes to take effect.
After Editing Registry (I changed the Default Decimal Value 96 to 150)