How to change a folder icon on Windows:
- Right click the folder icon that you would like to change
- Click on Properties
- Select the Customize tab
- Click the Change Icon… button
- Browse for the icon that you would like to use as your new folder icon
- Click Ok
- Click Ok again
How to change a folder icon on Mac:
- Press Control and click on the folder icon that you would like to change
- Click Get Info
- Drag the new icon to the top left icon in the folder information dialog box
If you do not already have the new icons you can find some free icons for download at Icon Archive. This site offers icons for both Windows (.ico) and Mac (.icns) so you can choose the appropriate format to download.