Windows 7 Tray Icons Changer is a freeware from door2windows that allows you to change the default tray icons of Volume, Network and Action Center in Windows 7.
How To Use:
Run the tool as administrator.
Select the icon that you want to change.
Click Change Selected Icon.
Select the new bitmap and click Open. If you don't have any icon, get some from here.
Now Windows Explorer will restart and you will be able to see the new icon.
To restore the original icons, just click Restore Original Icons.
In case anything goes wrong, just follow the steps in the following link to restore everything back to default easily: http://www.door2windows.com/windows-troubleshooting/